Thanks again for the tips. I have no idea what a 'blosk' is!!? May be I meant the 34pin ATX connector?
The PSU in it at the moment is 350w, I tried a 300w PSU and got some life but still not quite right. Went back to the 350w PSU and the LED on the switch is now lighting up but everything else is still dead.
However, after much thought, I have decided to go for a new PC. ASUS P5E mobo, 2GB DDR3 RAM, ATI 3850HD DDR4 graphics card. All the stuffs arrived today, so we will be gluing it all together tomorrow. Wish me luck