Hello everyone! At the request of the great Zinga himself and after extensive testing and furrowing of eyebrows I am proud to present my ISO guide:

Common and Not-So-Common Solutions to All Your ISO Issues

Getting your ISOs to work can be a pain in the a**, so here's a list of rules and solutions that should hopefully cure what ails yeh.

THE 3 RULES

Rule #1: Use a Frakin' UMD!
Switch "No UMD" OFF in the recovery menu and have a UMD game in the drive. This is the most important rule of them all and must be adhered to no matter what the circumstance. There's just some games out there that need a UMD so do yourself a favour and pop one in.

Rule #2: The ISO Folder Damnit!
This is more just to clarify things. All ISOs, CSOs, DAXs and JISOs go into the ISO folder on the root of your memory stick ie. ms0:\ISO

Rule #3: Latest is Greatest
Please try to use the latest firmware or loader. There's a reason why these things get updated so often so save yourself the stress and take the time out to upgrade.

Common sense people, that's the name of the game. If you've only just started learning how to use the computer then please take the time out to get your head around it all. You can't go from complete newb to PSP God all in one sitting. Have patience, some of this stuff can make even the most computer savvy scratch their heads in bewilderment.

Now, let's move onto solutions. There are way too many unique problems out there but most can be solved through the following solutions.

SOLVING THE ISSUE

Solution #1: Compress This!
There are a few compression types out there and some people get confused over this, so let me try to clarify things for you. The 3 main compression types are ISO, CSO and DAX. ISO and CSO can be played instantly in the latest OE firmwares. Of the two, CSO has the best compression so if you want to squeeze as much space onto your memory stick then CSO is the way to go. However DAX's compression is far more superior to the other 2. The only catch to this is that you'd need to use Dark_Alex's ZISO (link below) loader, but it's a small price to pay.

So now you're wondering how to change compressions, yes? Just download PSP Compressor from the link below and away you go. PSP Compressor allows you to change compressions to and from all three ISO types as well as JSO (though I personally don't know much about this format) so that oughta help you get the most out of you memory stick :)

So to further clear things up, I present to you this unspectacular ISO Compression Diagram

ISO - Lowest compression - OE Compatible (no loader required)
CSO - Medium Compression - OE Compatible (no loader required)
DAX - Best Compression - Incompatible with OE (ZISO Loader required)

Downloads
Dark_AleX's ZISO Loader: http://www.psp-hacks.com/file/498
PSP Compressor: http://www.psp-hacks.com/file/900

Solution #2: Where's the ISO?
So sometimes you download an ISO (as you do) and it turns out to not be an ISO at all. You end up with a file and a folder (UMD_DATA.BIN and PSP_GAME) that haven't been compressed into an ISO, so what do you do? Well there's a number of ways to make ISOs but for a sure-fire and problem free way then I suggest using UMDGen (link below). Sure you could use your typical ISO compressor bit UMDGen was made to properly compress the files into an ISO that the PSP can read. Once you've compressed then you can go onto compressing it further (CSO, DAX etc.)

Downloads
UMDGen: http://www.psp-hacks.com/file/194

Solution #3: Multiple Whatsits?
Has your download come in multiple files and you don't know what to make of it? Never fear, JP is here! The most common file splitting method is through WinRAR (link below). The easiest way to tell if they're RAR files is to look at their extension.

Quote:Tip: Make sure that you have file extensions showing. In any windows folder click Tools => Folder Options. Then click the View tab and scroll down a little way until you see "Hide extensions for known filetypes. Untick this if it's ticked.
(Props to Ryu for pointing this out)

If the extension files look like this - .r01 .r02 etc - then it's a WinRAR file. Download WinRAR if you don't already have it and once it's installed double click the first file (.r00). You'll more than likely encounter many different types of files and folders here. Don't worry about the clutter and look for your ISO, CSO or DAX (Usually found in an ISO folder). Now it's just a case of dragging and dropping the ISO out from the RAR and into the window of your choice.

On the (VERY) rare occasion you'll come across a different method of file splitting. If your extensions are just numbers ie. .001 .002 etc then it's in the 7Zip format. If that's the case then download 7Zip (link below) and use the same method to extract your ISO.

Downloads
WinRAR: http://www.download.com/3000-2250-10614813.html
7Zip: http://www.7-zip.org/

Solution #4: It Is The Fake!
In rare cases it is possible that you have a fake memory stick. I won't go into the specifics of finding out how as there are a few tuts floating around that do just that. So the question is - What if yours is fake? The issues that a fake memory stick can bring are varied but let's see if you can't get at least some use out of it.

First off, give your memory stick a Complete Format (not Quick Format) through Windows. Once it has run its course then format it again through the PSP (This mainly creates all the folders it needs to read the memory stick). After all that is done, throw your ISO onto there and see how it goes. If it works, then great! You don't need to go any further. If not, then I'm afraid to say that you're holding 512MB/1GB/2GB/4GB worth of dud memory - sorry :(

Solution #5: Tweakage: PITA (Pain in the Achoo!)
(Please note that this may only fix some cases.)
This is one of the more obscure methods of running your damnably difficult ISO. Head on over to your recovery console (Hold R while switching on your PSP). From there got to Advanced => Advanced Configuration and enable the "Execute BOOT.BIN in UMD/ISO" option. Exit the recovery console and boot up the game.

Note: The drawback to this solution is that you'll find some ISOs won't work when they previously did. In this case then disable the BOOT.BIN option in the recovery console. It's a pain, I know but at least you're able to play that difficult ISO.

Solution #6: Still Not Loading ARGH!
(Please note that this solution only works on about 60% of bad ISOs, not much but it might be the cure to your problem)
So you've gone through this whole FAQ and still come up trumps on loading your ISO? There's only one reason left for this - bad compression. This is not a fault on your part however. Whomever uploaded the ISO has obviously compressed it using an unsupported ISO compressor and it is your unfortunate job to set things straight.

So first thing's first, extract all the files from the bad ISO using WinRAR (link above). After extraction you should have a file and a folder (UMD_DATA.BIN and PSP_GAME). If you don't get any files like this then the ISO was a dud and you were robbed of however many MBs it took to download it.

Now all you have to do with these files is compress them into an ISO. Boot up UMDGen (link above) and drag both the file and the folder into the window that reads "no items to show". All that's left to do is save the ISO (name it what you will) and let it do it's compressing. A few minutes later and voila, you have a readable ISO for your PSP. From here you can change the compression to your prefered format using PSP Compressor (link above).

Conclusion
Well if you follow these guidelines then you'll hopefully live an ISO-issue-free life. I don't claim to be an expert but I do know what works, so hopefully my shared knowledge can help people get the most out of their gaming time and spend less time stressing out on the Help forums waiting for replies.

If anyone has anything to add then let me know and I'll edit the post as necessary.

Hope to have helped.

JP