Just now, as I switched on my main computer, it powered up for a second then shuts down - but the light remains on on the power switch. Tried this for a few times.
Since I've laid it on its side it now just keeps rebooting, and not loading up windows at all. Although it goes as far as the Windows XP logo, but it fails to fully boot up to windows and restarts again. It doesn't even boot up to safe mode, but it can boot up to BIOS.
Is BIOS set to HALT on all errors? if so turn that option off and then see what, if any, error message is displayed on screen
Also remove harddrive and see how far it gets (should get to stage where it tells you 'no bootable media)
Also reseat the RAM sticks, and try with only one stick in at a time (one of them may be loose or faulty) check all other connections (especially after you have had it upside-down.... robinofloxley[grin]) and clean out any muck and dust from inside casing.
Switch off and disconnect mains plug between each of the above.
When you want to switch off hold in the power button for about 10 seconds.
I went through the procedure above and the problem still remains, I disconnected the hard drive and secondary drive - with the HDD disconnected a message came up saying no bootable disk or something, with the secondary drive disconnected the problem remains as above. With the memory unseated there was one continous beep. And I hoovered all the dirt out and yet nothing has been solved. And yes that was the message I was getting on a blue screen after trying to use anything like recorvery console