Question Advent DT2111 - Turns on and off again. Works then doesn't.

Sep 23, 2020
Hey there folks, long time using the website for trouble shooting, first time poster.

I have a problem with an almost stock Advent DT2111.

i5 2320 3.0Ghz
AMD 6670DH
Foxconn h61mxl/h61mxl-k motherboard (not sure which one as of yet)
500gig SSD
Two power supplies

Let me explain whats happening. I recieved this machine off of a friend and got it working by adding nothing more than a spare PSU. Was happy with itself and done it's job fine. Eventually it just stopped working one day. I assumed it was the power supply but wasn't in the best financial position to afford a new one. Out of nowhere the PC started working again for a couple of days till it decided that it didn't want to anymore (will continue to turn on after not being powered on for a period of time - days). I replaced the PSU with a throwaway I found and it was working fine again. 3 days of use including working from home. Same problem arises that it refuses to power on. Seems to be the same problem again.
PSU seems to be working as the mouse lights up and keyboard etc
Press the power button and the fans on the heatsink and the PSU spin for about a second or two then stop and tries again. It now does this in an infinate loop of trying to power on, spinning the fans then stopping.
I've been through the forum and tried several things.

-I've replaced the CMOS battery (that was a pain to try to find at 10am this morning)
-Cleaned the RAM, switched the sticks - tested them etc.
-Jumped the CMOS jumper

It probably will work again fine in a couple of days but I need it to be more reliable as it put me in a position with work this morning.

Any ideas or input would be greatly appreciated.

Thank you so much in advance.