System BSOD at Shutdown

[Mad-Marty]

Hi,

i've a strang Problem with System crashes out of nowhere - System worked in this configuration for over a year.
Since a few days the system crashes after logoff right before turning itself off with different BSODs.
There's no clear pattern for the BSOD and driver type it crashes at.

OK so i thought might be the CPU which has degraded or something like that ... primed ... 20 minutes ... nothing.
Next step Memtestx86+ ... nothing again.
Then some tests for the crash again ... start - logon - shutdown -> bsod ... this is absolutely repeatable.

Then some problems with SSL connection started , https pages not loading for example.
Lowered CPU clock by 100 Mhz ... everything works again for a evening.
But problems came back after a while.
So it doesn't seem the CPU after all.

I suspect motherboard or PSU. A quick look at the mobo revealed no exploded capacitors.
The crashes never occur on load, e.g. while gaming. But basically always while Shutting down.

The PSU is quite old, around 6+ years i think. (Tagan 530W, not the best overclock PSU but not really bad either, 2 12V Rails and plenty of Amps).
Voltage reports seem good though, but maybe there is a short dive suddenly which crashes the system?

Does anyone know if PSUs exhibit this kind of degradation where they suddenly can get problems providing clear power for the system?
Did someone else experience the same and has a hint of whats wrong?

I also dont believe in file corruption. Files seem to be ok. And it does BSOD from IRQL_NOT_LESS_OR EQUAL to various drivers.


TIA