I have hear about this error before but only in windows 2000 without service pack 1 (service pack 1 solve the problem)
Also some people have reported this problem when using hyperthreading (You have a celeron so thi isn't your problem)
Mircosof words for this problem are:
CAUSE
This behavior occurs because the operating system does not allocate a large enough buffer for the maximum string length permitted. When the data is greater than the buffer size, the Winlogon service terminates abnormally and your computer generates the error message.
Mirc by itself can't cause something like this .Do you use a script?A script with some "unknown" and not well tested dlls can cause memory errors
If you don't use a script maybe it is something wrong with your OS.Installing your OS again every 6 months is always a very good idea
Finally do a memory test ,but i dont believe it is a hardware error.Just do it to be 100% sure
