Ok say I'm back to face my limping PSP. I cranked everything up and got ready to try and breath one last breath of life into it... and it worked. BluDevil, I followed your quote and it appears my settings were different to the ones you've shown - interesting because I'd not been into that particular menu once (the word 'advanced' scares me). But nonetheless, I set it up as shown et voila! I'm back in happy land.
Amusingly my PC crashed out and had a RAM failure when I connected my PSP to it so I had to fix that mess before I could start back on the PC...

Once again guys, thank you all very much in guiding me, a complete stranger, through a harrowing time when I thought my favourite toy was fuct.