[fitkoh]

Any suggestions what should i do before i send it for repair?

I think what I would try if you know someone with a pc that can use the same ram and swap it out and see if you can run ram memtest on it.

In your system settings (or whatever it's called on windows), does the system report the proper amount of RAM?

Your PC could be overheating but unless the thermostat is broken you should be able to check your cpu temp. Also, if it's overheating I think the pc will simply turn off, not freeze or hang.

Also, as you seem to be comfortable working inside the pc, you might try just buying a stick of ram (buy one with a good return policy) and test it out. If the new ram solves your problems you can avoid an expensive repair bill. If not, return the new ram and maybe consider sending it for repair. Although I wonder: the i5 is a somewhat dated processor... it might cost more than the pc is worth to have it serviced.