Pc trouble with booting up and random freezes

[Proximitus]

So, I did a clean install of my pc because it was behaving weird. Sadly, it didn't help..

 

Usually every day when i boot up my pc, it won't beep once, to let me know everything is alright, but, sometimes it does. When it does, it's booting up correctly, sometimes freezing at my desktop, sometimes working like a charm for 9 hours straight.

 

The problem is, I brought it to a shop to check on it, but they couldn't find anything! It worked perfect. No RAM failures or such. The only difference is that they didn't connected the cable of my power supply (they had their own) and the cables of my monitor and mouse etc.

 

I've googled around and came across something called Power on Self Test, or POST. Apparently, that checks of everything is worked correctly when booting up. So I was wondering if I could view the logs somewhere, to find out what causes this.