And it's getting close to moving Arunion's hardware troubles to a separate thread.
But out of interest, here's my quick summary of what 20 years of investigating malfunctioning PC's has taught me:
- PC randomly reboots, or fails to boot: PSU. Can be motherboard, ram or cpu, but the PSU is the most likely culprit here.
- Applications randomly crash: RAM, maybe cpu.
- Games randomly crash: graphics driver, maybe RAM (and I had one that was down to a faulty memory controller on the motherboard!)
- Slow system response, things freezing for many seconds: windows is waiting for something to respond, but it fails to. System times out and continues. Software configuration, hardware configuration, driver problem, especially graphics driver, sometimes network card. I've had this happen from a hard drive that failed to wake up when asked for data, and from software attempting an automatic internet connection but failing (causing a delay while it waits). But probably not a hardware failure.
- Applications, even windows, does not load reliably or correctly, but issues are random and unrepeatable, often with strange memory warnings as it crashes at start up: loose HDD cable. This one can actually cause ALL of the above problems, so check it first - it's a free fix if it is the problem. SATA cables are really bad for secure connection - I've had one that required duct tape to keep it attached. And the "clip" type are better, but not always a fix, if the socket itself has nothing for the clip to grab on to. Some hard drives are like that.
It is dangerous to write any data to the drive in this condition, because it will almost certainly be corrupted as it is transferred to the disk. I stopped one guy from reinstalling windows in the nick of time - he'd have totally trashed what was a healthy, working installation.
Always check for a loose cable first, and reseat the thing at both ends anyway, just to make 100% sure.
Arunion's issues are most likely a graphics driver problem, possibly worsened by a loose hdd cable that may have been nudged while the graphics card was changed. But almost certainly not the PSU.
.Ill not hold my breath on this one 
