Sorry for the delay in my response. In my experience, "freezing" occurs as a result of several reasons. The graphical failures you experienced could also be an indirect cause or result of some other more probable failure. The typical reasons for failure are:
1. RAM - Like anything else, RAM isn't immune to failure, even if it were working a minute prior, that doesn't mean that the RAM isn't failiing.
2. CPU - Probably the biggest CPU failure is in the heatsink fan. The CPU is designed to shut itself off when it 'senses' immenent failure; not just the actual failure itself. Meaning, if the CPU is heating up too fast, it will also shut down.
3. PSU - Probably the second most common failing part is the PSU. It goes without saying that improper voltage or load will cause system failure, but testing the PSU's P1 connector is the best way to determine if the PSU is still good.
A distant fourth culprit could be the GPU that causes freezing, but you'd more than likely experience BSOD after BSOD if the GPU starts to fail.
Unfortunately, the only way to test the CPU is to put it in another mobo and see if you can get a display then; or use a different CPU on your current mobo. If you can get your hands on a different mobo, I would also test the RAM using MemTest86+