I think his computer is restarting due to a fatal error which would usually bring up a BSoD, but it isn't because it's set not to.
I don't know how to change it from 'restarting' to 'show the Error', but I found:
Automatically Restart
Under System failure. Right click my computer and properties, Advanced , Press settings under 'Startup and Recovery' and UNtick the box Automatically Restart.
When he crashes and reboots in Gmod again (Which he should purposely do) it should show a bluescreen with some info on the error.
Possibly a filename at the bottom, and a STOP code in the middle, which is something like:
STOP 0x000004E
Post that error back here if all the above works.
Stop 0x0000008E (0xc0000005,0xBF0BDF21,0xBA6349CC,0x00000000)
ialmDD5.dll adress BF0BDF21
BASE AT BF077000 DATESTAMP 00000000