Ah, if the original drive had the same symptoms as the SSD (ie. would not consistently be recognized by the motherboard), then it's probably the motherboard. If the original drive simply showed periods of freezing/hanging, it could just be that it was failing, and the SSD is not compatible with your motherboard.
Another thing you could try is to run some diagnostics on the original drive to see if it is failing or not.
Here's a link to some WD diagnostic software. Get the version for DOS on CD. That way you can boot from CD and have it run on the computer itself. Good luck!