Computer keeps on restarting

[Guest]

Hi,
i need some assistance regarding this problem i encountered recently.It
all started after i updated my Windows XP to Service Pack 2.Initially,it
works well.But,afte sometime,my computer restarted all of a sudden.When it
entered,the window logon screen.There is a pop up :"lsass.exe fail to start"
or another message regarding lsass which i didnt manage to catch.From then
on,this problem keep on happening and at one instance,during scandisk,it
stuck at 5% and freeze.In the end i had to reformat my computer.I borrowed
another copy of windows XP from a friend of mine and reinstalled it but the
same problem still occured.When i check the event log i got a warning message
with the following description:

ID: 1517
Source: Userenv
Version: 5.2
Symbolic Name: EVENT_HIVE_SAVED

 

[Guest]

First of all i would like to thank you all for replying.Although the
isass.exe problem was solve , the restarting problem still persist.I am sure
that the problem is not cause by sasser or any virus.I follow the instruction
from one of the post and disable the auto restart and i got this blue screen
with the following description
:"C000021A Fatal Exception Error 0X00000401(0X00000000 0X00000000)".Because
this restarting problem occured randomly,i didnt manage to get the time of
incident.
But at one instance,i did managed to take down the time and found something
strange.Everytime before the restart occures , these 2 event were record in
the event viewer :

"wuaueng.dll (2324) SUS20ClientDataStore: The database engine started a new
instance (0)."

"wuauclt (2452) The database engine 5.01.2600.2180 started."

After i did some checking in the system32 folder and found wuauclt1.exe and
wuauclt.exe(system is using this) and that goes for wuaueng.dll.

so i guess the problem might be cause by these...

i hope you guys can provide me with some assistance again

meanwhile i will try to overwrite the files.