Very frequent BSODs and lockups, lockup even in safemode

Here are my dump files. The main errors are Modification of critical data or system code. I was trying to recover the files in safe mode using DM log collector, and it locked up in the last part of the process. I've run Memtest before, and had a full pass, but then a lockup during testing. There are periods of time where it runs fine for ages, then it will suddenly crash lots of times in quick succession. I've also tried the /scannow command again, that fixed it last time for about a month. Not sure what else to try. Any help would be greatly appreciated.