How can I test out a used computer to make sure it is fully functional/ with no problems?

[TonyTheBulgarian]

Basically I am getting a really good deal on a used PC. But before I actually purchase it I would like to test it out with programs that stress it/ check for any errors/ see if the components are fully functional. My question is which programs should I get? As in what program would be quick enough to where we don't have to sit around and wait for a whole game to download so I can test the CPU/GPU

 

[Hellfire13]

stress testing applications...

prime95 for cpu
memtest86 for ram
furmark for gpu
harddisksentinnel for hdd
http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html for psu


you can google about these if you want any more details...