PC Rebooting (no error)

[Czlee]

Before I start let me post my specs:

MSI RTX 3050 X 8GB

Intel i5-9400f

MSI Z390 A-Pro

500gb m.2 SSD

750w 80gold EVGA Psu

 

i decided to upgrade my cpu on a budget just for streaming, I had a i3-8100 and it couldn’t stream duh with 4 cores. However I went cheap and ordered a Used - Like New cpu(i5-9400f for like $89) off of Amazon, install went clean other than the fan wouldn’t mount but I ended up getting it. At first I got stuck into immediate reboots, no error code, just straight from my desktop to startup just on a loop pretty much. So I updated my gpu drivers on safe mode, and I don’t know if it was by luck but my pc started working again, I launched up discord and stream labs and I streamed MWII with my friends for 3 hours, no problems. I ended stream and went outside to take my dog out, and what do you know, I come inside to my pc rebooting again. I took it to a shop they said it was the OS, so I trashed my HDD because it was old and went out and bought a M2 installed it cleanly and loaded up a fresh W11 OS. Went smooth for about 5 minutes then another reboot loop started happening. I put in my girlfriends 1650 super and it was fine again, but nope 15 min later it started rebooting. So now I’ve lost all my files , bought a new m2, and all I wanted was a new(ish) cpu. My pc hasn’t worked for more than 20 min since the cpu install, tomorrow im taking it out and putting the i3 back in just to see if it may be the USED cpu my cheapo self bought preowned. Has anyone ever ran into this problem? If you have how did you resolve it? Im pretty close to giving up and rebuilding my whole machine (which will take a while bc I just moved and moneys tight hense the used cpu). Could I have somehow damaged the mobo , even though I was very careful on the install, let me add also my cpu temps sit around 32 Celsius, same with gpu (while idle, which is what it is when it crashes. Idle not being used). Someone please help. 

[WoodenMarker]

If the issue started occuring after a CPU swap, it's probably the CPU. Try reseating it and making sure there isn't any dust in the socket or on the pads.

You can also try swapping to the i3 and seeing if the same issue pops up.

[Ozymondias]

I would switch back to your old CPU and see if the rebooting issue persists. If it does, chances are your used cpu... well, has problems.

Make sure all the contacts are clean; do a reseat, make sure there are no bent pins, andthat the thermal paste/cooler are attached correctly. Also, reset the cmos battery. Couldn't really hurt