and I can't believe what it was...lotvic, it was what you said.
The side panel that has to be removed is on the opposite side to that of my computer which made me take the wrong side off at first. When I put it back, it hadn't slotted into the front panel correctly. This must have caused a problem with the power switch as when I did slot it in correctly, I could tell that there was a difference by the feel of the power switch. The computer booted up fine and now the wireless network is up and running :o)
It's amazing how easy you can overlook the basic things and start trying all the technical stuff - I had allready before that started removing things like the graphics card and RAM to see if they were the cause incase I had zapped any with static that may have built up inside me as the computer was in the attic so there was nowhere I could earth myself.
I had the same problem with a Packard Bell. It tirned out to be the power switch on the front, the micro switch had popped out of its mounting, due to someone with a heavy finger. If it is difficult to get to, trace the connector to the motherboard, lift it of and short the two pins on the motherboard momentarily if it then powers up the problem lies with the switch.