I heard a strange whining noise every time I started my computer. Suspecting that it was an old hard disk going, I opened the back of the box and unplugged the hard disk to see if there would be less noise, which there seemed to be. At least found out that the noise was not the fan. But now my computer refuses to start up, even though the indicator lights on the motherboard are on, and as usual the indicator light beside the on/off button at the front of the computer comes on when I press it in, and goes off when I hold the switch down…. Could not find any loose cables. Could I have jolted the system with static (if so why are the indicator lights working as normal) or somehow short-circuited the system – or could this mean that the hard disk has given up the ghost…hmmm. What would you do now if you were in my shoes -- apart from kick myself?

If you pulled the plug off the hard drive with the power on that was not a good move. If you turned power off before its probably the drive finally given up the ghost.

GO back in and make sure the cables are tight on the Motherboard as well as the Hard drive. And Ron is correct, never pull the plug on anything while it is running. IF you touched something inside the case without grounding yourself first, that could cause the problem. Is the PC booting and you just don't get any picture? May be the video card got loose. Check everything inside(using Anti Static Measures) and re-seat everything.