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...