As per Microsoft Developer Network: (http://msdn2.microsoft.com/en-gb/library/ms795746.aspx)
Bug Check 0x7E: SYSTEM_THREAD_EXCEPTION_NOT_HANDLED
The SYSTEM_THREAD_EXCEPTION_NOT_HANDLED bug check has a value of 0x0000007E. This indicates that a system thread generated an exception which the error handler did not catch.
Parameters
The following parameters are displayed on the blue screen.
Parameter Description
1 The exception code that was not handled
2 The address at which the exception occurred
3 The address of the exception record
4 The address of the context record
This is a very common bug check. To interpret it, you must identify which exception was generated....
0xC0000005: STATUS_ACCESS_VIOLATION
A memory access violation occurred....
...If a driver is listed by name within the bug check message,{We know that it is pci.sys} disable or remove that driver. Disable or remove any drivers or services that were recently added. If the error occurs during the startup sequence and the system partition is formatted with NTFS file system, you might be able to use Safe Mode to rename or delete the faulty driver. If the driver is used as part of the system startup process in Safe Mode, you need to start the computer by using the Recovery Console to access the file...
On This Site: http://www.techspot.com/vb/topic30132.html
It is recommeneded that you "Reseat the memory stick to another slot. Clean the dust inside the PC. If it still crashes, downclock the RAM. If it does not resolve the problem. replace the RAM."
Could also be that you are using XP SP1. SP2 includes a fix for this when caused by certain issues. http://support.microsoft.com/kb/811113/en-us