Custom built PC, illogical fails

Hey guys, so, my PC is custom built, I built it myself after carefully learning about which components would match and such.
This was about four years ago.
After a while, about one year ago, it started acting up, random shutdowns, blue screens, freezes. I thought it was due to overheating (As speedfan showed me that my CPU was on fire) so I cleaned the old thermal paste, cleaned the cooler, replaced it with new paste. That's when the trouble started. I tried to start up my PC, the CPU fan was spinning, but there was no POST (And no display). After a dozen restarts, it finally booted up. I could shut it down and restart it without any trouble. After a while, I bought some new RAM sticks, put them in, once again, no POST, no display, CPU fan spinning. After carefully looking around the PSU, I saw that it had a broken coil, so I went on and changed the PSU.
A couple of months later, tested a GPU for a friend, put mine back, once again, no POST, no display. After looking around the MB, I saw a broken capacitor so I went on and changed the MB.
Ever since, everytime I clean it (As in remove the pieces and clean them individually, of course, after discharging myself electrostatically, removing the power and waiting for the capacitors to drain) the same thing happens, no POST, not Display, for a long time. CMOS reset does not help (Nor removing the battery nor using the jumper). Sometimes it gets fixed if I let it shut down for a couple of hours, sometimes if I let it run, sometimes if I take out a RAM stick, sometimes if I remove one HDD.
My question is, is it possible to be because of the CPU? Now, when I cleaned it, I saw that some thermal paste made its way onto the CPU pins, most likely short-circuiting a couple of them, however I have no problem whatsoever (No lagging, no BSOD, no freezes, no random shutdown, nothing) unless I replace a component or take it out and put it back again.
I connected a speaker, if I remove all RAM sticks, the 3 beeps are there, which lead me to think that the MB works fine (Also, considering I had changed it a short while ago)
After removing one of the HDDs, it booted, I let it turn on completely, shut it down, plugged the HDD back in and it worked.
My current configuration is:
CPU: AMD Athlon II x2 245 2.9 ghz
RAM: 6 GB RAM DDR3 1800 ghz
PSU: 500W
MB: AsRock N68C-GS FX (Dual Channel)
GPU: Nvidia GT 220

I am sorry if I posted this in the wrong forum! Thank you in advance!

breaker,
Not sure where to start but the fact that so much thermal paste was applied it rolled over the side and found it's way to the pins is very disconcerting to me. I would start there and remove the CPU and get a bright light and a magnifying glass to look for paste in the sockets as well. Was this issue found on the original mobo or number two mobo? Are you saving possibly for a new build as it sounds like maybe it's a good time to upgrade both the mobo and CPU. I can't stress enough that less is more when applying thermal compound. Next have you run memtest on your ram, if not then now is the time. If upgrading isn't in the cards then I would remove everything out of the case and bench test then carefully install all over again as I suspect a possible extra standoff under the mobo so counting up and triple checking is in order.

linnemeyerhere said:

breaker,
Not sure where to start but the fact that so much thermal paste was applied it rolled over the side and found it's way to the pins is very disconcerting to me. I would start there and remove the CPU and get a bright light and a magnifying glass to look for paste in the sockets as well. Was this issue found on the original mobo or number two mobo? Are you saving possibly for a new build as it sounds like maybe it's a good time to upgrade both the mobo and CPU. I can't stress enough that less is more when applying thermal compound. Next have you run memtest on your ram, if not then now is the time. If upgrading isn't in the cards then I would remove everything out of the case and bench test then carefully install all over again as I suspect a possible extra standoff under the mobo so counting up and triple checking is in order.

Thank you for your reply! The thing is I applied really little thermal paste, and there was none that was getting out, even after squeezing the fan on top of the cpu; it is in the second mobo; I checked the socket with a magnifying glass and there was nothing inside, else I would've changed it.
I thought that maybe the heat made it melt and it went down to the pins, which really concerns me. At the moment I am trying to save up to change everything, not just the cpu or mobo, but I still need a couple of months before reaching my goal. I've run memory tests and the memory seems to be ok. It's not the first time I changed the thermal paste, and this has never happened to me before.

Can you post some detailed pictures of the inside of your rig? How many hard drives and what type?

I am sorry for the delay, my MB blew up and didn't manage to get a new one till now. Apparently it was a MB fail, once again, even though it was relatively new. Changed it and it works like a charm. Thank you for your time!

Thanks for the update and glad all is well !