PC keeps rebooting, then stops...

This puzzles me and don't know where to start, or rather continue to troubleshoot. The PC in question has:

• Core i5 2nd Generation CPU (Sandy Bridge)
• 8 GB memory (2 x 4)
• 2 x 256 GB Samsung SSD
• 1 x 1 GB Seagate HDD
• 1 x CD/DVD drive
• 1 x 650W power supply

The PC runs W10 Professional 64-bit, version 1803. The last time the PC case had been open must be 2-3 years ego, but opened today. The PC had been moved about 9 month ego to its current location.

It has been pretty much trouble free, until last week. The PC starts up, boots Windows, presents the login screen, but by the time the credentials entered, the system reboots on it is own. After the second and subsequents reboots, it reaches to the point that Windows does not finish to load or it doesn't even start loading and just reboots. After "n" number of reboots, the system does not boot anymore.

Leaving the system down and shutting off the power switch for a longer time period does allow start up again. Entering in the BIOS at this time gives just enough time to get the MB and CPU model numbers and it reboots again.

Opened up the case both sides and verified that all five fans are running, as soon as the system is started. Disconnected all of the drives and started the system, the BIOS stated that "No bootable device found..." and back to cycling reboots.

Reset the memory, tried booting with just one memory card, remove/reconnect power cables to the MB and video card did not matter, the PC is cycling reboots.

There's not enough time to do any troubleshooting with the cycling reboot, the system does not have any beeps or otherwise indicating issues.

The plan is to reset the CPU and if that's not resolving the issue, replace the power supply. If it's still having the same issue, replace the CPU, MB and memory.

Prior to going there, does anyone have a suggestion how to verify the source of this issue?

TIA...

Geosammy said:

When you say "reset the memory" do you mean,
that you re-seated the modules themselves into their slots?

Yes and also tried starting with one memory card only, once for each card...

Did you check that all the cables for the drives and anything else,
are firmly seated into their correct ports?

Yes and the system had been booted without any drive connected, both the power and data cables disconnected...

Could also be, (as you may have surmised), a power supply issue.

Well, the power supply is 6-7 years old. Replacing it should not be a big expense and if the system is rebuilt, I would need a new power supply anyway, would not use the old one....

Geosammy said:

Did you remove and reinstall, or replace the Cmos battery?

If so, then you've tested just about everything you could've, barring the motherboard and PSU.

Thanks Geo...

The Cmos battery had not been touched as of yet, could that cause this issue? I don't have one handy and not certain, if just remove/reinstall would have any effect...

Removed the battery, CR2032 and measured the voltage; it's at 3.15V DC. Reinstalling the battery forced me to enter the BIOS at the first time the PC booted.

I am in the process of resetting the Noctua heatsink, that didn't even have much dust in the heatsink fins. Not too bad for 6-7 years old PC, just love the dust filters on this case. On the other hand, CPU and the heatsink surface looked dry. Cleaned it up and about to put it together with Noctua's thermal compound...

Thank George...

Unfortunately, that has not been the case and I should have known in advance. Once I've got to the BIOS, the CPU temperature was 87 degree Fahrenheit.

About the power supply...

A power supply for an ATX motherboard is the same regardless, if the MB is for Intel or AMD, right?

The reason for asking.... If the new power supply does not fix the issue, then need a new motherboard, CPU and might as well DDR4 memory. I'd rather go AMD in that case....