I've built two similar Hyper-V servers. One is OK but other Windows Hyper-V Core fails in 1~4 days (BSODs with different reasons).
The only different parts are CPU & RAM. Now I'm testing the failed server with MemTest86+ and got an error; Test:8 Pass: 0 ...etc Count: 1
Is this error fatal? There are 4 modules of 4GB RAMs without ECC.
You call the company that sold you the box and ask for warranty. They should replace the RAM.
You ask what you do? You replace the RAM.
Still got the error? Make sure you're within specs (don't use cheap-ass RAM. Sometimes, manufacturers impose certain requirements on their OEM parts. Make sure the RAM is made for that particular machine. A prominent example is Apple, putting cheap ram in those, even when matching the OEM clocks/timings guarantees a BSOD, even when it's from the OEM itself. Get a certified one from the OEM, it works).