Win xp home fails to boot
 

A winxp home machine which has run fine for months
suddenly began rebooting without warning during use.
Fairly soon it would not boot at all. I presumed a power
supply problem and replaced it. The PC did in fact then
boot into the choose user account window and then shutdown
(not reboot). The PC is fine in safe mode but only the
administrator and the main user account appears and the
other 3 user accounts are missing from the choose user
account screen. I have since spotted the reboot on error
function in winxp and have disabled it. I have tried to
use system restor but whilst appears to restore the files
when it reboots it crashes(powers down) again and in safe
mode it tells me that the system restor failed. I have
tried restoring on all available dates but they all fail.
The event log reports volume shadow copy service error-
unexpected error calling routine CocCreateInstance
hr=0x80040206 & the com+event systemdetected a bad return
code during it's internal processing. HR result was
8007043c for line 44of
d:\ntlcom\com1x\src\events\tier\eventsystemobj.cpp

Can anyone help me please?
Trevor Gale