Well, I should've included the PSU in the specs. It's a three-year-old
Dynamo 500w with a single large fan on the bottom, and it was a leftover from my brother-in-law's previous dual-core (and heat-prone) Pentium 4 machine before he had this PSU transferred to the current machine.
Turned out that as I opened up the machine and checked the CPU, the stock thermal paste had dried out completely, and so I gave a new daub of fresh grease (fortunately I managed to keep this in a mobo box three years ago).
So far, I'm seeing if this machine would be doing fine again, along with some power-management and cooling adjustments in the BIOS, as my sister's family has an intense love for Facebook's games from 7 in the morning till 12 midnight, more than my love of MMOGs (shakes head).