XP hangs during boot

Hi,
I need a bit of help. I have a home built computer (Asus Mainboard, AMD Athlon) which has been working wonderfully since January.
Yesterday, while in normal use it hung and on rebooting it reached a point in the reload where the main switch clicked off and immediately on again about every three seconds and the only way to halt it was to reset. The same thing happened again and turning the power off was the only way to break out of the cycle.
The same thing happened when I tried to run in safe mode.
I put the XP CD in the slot and it began to load windows and hung again apparently at the same spot in the boot.
I tried booting from a floppy and got a string of log records that ended with the Mup.sys driver.
I tried this three times and each time it got into its switch loop after Mup.sys.
I went into the bios and quizzed the data on both HDDs and they seem to be ok.
Afraid this one is beyond me. Can anyone help?

 

Open it up and see if there is dust built up in the fan/heatsink causing overheating. Check all connections to see if any are loose. Reseat all cards including memory. Test the power supply.

 

Mup.sys? This is page 21 of 25 (!!) about Mup.sys:
http://www.hardwareanalysis.com/content/topic/31874?o=400
More:
http://www.annoyances.org/exec/forum/winxp/t1047532372

They all pretty much relate to hardware.

It may be that Windows loads the drivers for particular hardware (no problems), but when it gets to loading the desktop, the drivers won't run the hardware. Mup.sys was just the last entry in the log (from what I read).

You cannot get to Safe Mode so best thing to try would be to remove all non essential hardware. Pull out and reseat the connectors for the drives, RAM and graphics.

There is a hardware communication problem somewhere.

Matt