Did you also install the latest nForce drivers from Nvidia? n650 chipsets are pretty terrible (not just because they're old. they weren't very good from the start) - you may want to switch the motherboard to something more modern so that you can get AHCI and trim for your SSD.
Thanks for the reply.
Turns out the drive is fine. This is actually a known compatibility issue with nForce chipsets that there are no plans to resolve. Tried a few workarounds, but no luck.
Fortunately my brother happened to have a system with a very similar CPU with an Intel-based chipset. Swapped computers with him, switching over the memory, hard drives and video cards - works like a dream.