Windows XP Home hangs frequently

[=?iso-8859-1?Q?Jos=E9_Castelo_Branco?=]

Windows XP Home hangs without notice. Only stops and I
have to shut down the computer.
I have a IBM HD with 40 GB. The Disk Fitness Test doesn't
find any mechanical error.
Also Scandisk doesn't find any errors during surface
scanning.
I wiped the HD with zeros, formated it and reinstaled the
Windows XP Home, but the problem is the same: after a few
seconds Windows stops.
I did the same and I did instal Windows 98. No problems...
Can somebody tell me what happens.
Thanks.

 

[JCB]

It seems to be the RAM memory.
I try to run the Windows Memory Diagnostic and it stops
on Stride6 test.
I'll replace the SIMM tomorrow.
If this correct the problem, I' tell
Thanks.