Format your box and install Windows 2000!!

550 Mhz is just to slow for XP
and also 128 MB is the absolute minimum for XP
I beg to differ...

When running a computer on 433mhz and 128mb ram before i got a new machine, i found it to be adiquit and never crashed once!

How old is this machine? Sounds about 3 years old to me... some of the hardware may be on the way out, ie: the motherboard and/or the hard drive.

Try re-formatting with XP, if the keyboard is working again then carry on as normal... if you find that this happens again i suggest you backup your files and look to invest in either some new parts or a new box.

I would also suggest tweaking for optimum performance and lower the amount of resources being used at any one time... take a look over at http://www.tweakxp.com for some useful tips and tweaks.