OK, we've got a cooler that looks tightly installed.
Since you applied thermal paste, I assume you aren't using the stock cooler. What cooler are you using?
Did you remove the plastic that protected the base of the heat sink during shipping?
When you say the thermal paste "got smeared a bit" . . . if thermal paste is applied too heavily, it can act as an insulator rather than a conductor of heat. Did you put on a thick coating? or what?
Anyhow, remove the revodrive and boot up. Use what little time you have to download CPUID's Hardware Monitor, and get it running. Watch cpu and gpu temps until the PC fails. See if those correlate to the failure.http://www.cpuid.com/softwares/hwmonitor.html