Office PC's are always clogged with Dust and Dirt. First thing you want to do is install a good temperature monitoring software : SPEED FAN or PIRIFORM SPECCY.
Any of these 2 should tell you your current temperatures on the PC. If they are anything above 45-50 Celsius, buy a can of compressed air, open PC up and then clean the following: Heat Sink Fan, Case Fans, Power Supply Fans and also any dust in and around the Case.
Also check all connectivity cables to make sure none of them have a loose connection. Check all cables inside of the case to make sure none of them are caught in any of the fans or trapped on a heat source.
Check your temperatures again and report back if possible.
Good Luck !