computer overheating -> shutdown

Hello, thx for reading!

I have a 3.4ghz i7 pc with decent air cooling fans, about 4 years old. recently it became very slow, and i tried EVERYTHING to fix it -> clean pc, deinstall all, fragment, registries, avg tuneup and lots more tools. Performance increased somewhat but seemed to still go down over time. I ran hardware checks on everything, all seems ok, removed and cleaned dust again.

With the last, more rigorous clean, performance somehow went up, but just before that I had 2 automatic shutdowns after running very slow all night with just a browser open. Since I've been running a program called Prime95 that does a stress test, but during the first run it shut down again.

I used speedfan to monitor the temperatures, and it seems bugged (see screenshot). I added HWmonitor and it claims my CPU temperature is about 55-60 degrees in rest, but during the Prime95 run it slowly shoots up to 97 degrees!! (all temperatures in CELSIUS). I think 105 or so is automatic shutdown temperature for my board.

Speedfan says AUX temp is overheated, 70 degrees in rest going up over 80 on heavy load. then again it says CPU is -60 degrees, and it says my aux1 fan is off, which i think it isn't. All these numbers, the increasingly slow running speed past months, and the unexpected shutdowns that happen more often, worry me greatly.

Here is a warm ambient temperature of around 27 degrees, but the pc is clear and the fans all run. I have absolutely zero budget to fix this. Does anyone have any idea what I could do best?


The pc is rly fast, with overclock capabilities I did not even use, and the guy who sold it was sure it had the fans to support 4GhZ+ overclocking. I don't know much about all this, but I just can't figure out the real problem and thus the best solution.... I have done lots of searching online, also checked malware and virusses etc, tried everything... I'm getting pretty sure the slow performance and shutdowns are probably due to overheating. Any ideas/suggestions/help?? Would be greatly appreciated!

Mick

p.s. my first tech request post so hope the information provided is adequate/ not to redundant.





EDIT:


Thanks a lot for quick reply. Thats very helpful, I will have to get some paste somewhere.

I never opened the cooler though, guessed good quality paste should last a while longer? The pc has a high uptime, is it likely the thermal paste has just gone bad? It's the only thing I didn't try yet, for budget reasons, but I will then. Last questions:

Is it likely this will fix it? or just last option and no alternative?

Am I likely to mess something up and break it opening the cooler? It's how I lost my previous PC, since the paste stuck like glue and i had to rip it out kinda hardhandedly, but it was pretty old and it could just be another reason it didn't ever go on again.

Thanks again!
Mick