I understand that there are similar questions.

Recently I replaced my apple hard drive with a WD Black 500 Gb 7200 RPM hard drive when the apple one crashed. It has worked fine for the past three months until two days ago when I tried to boot up my computer and it went to a grey screen with a flashing folder/question mark and would not boot up past that. However, when I opened the computer and unplugged/replugged the hard drive cable back in, the computer began to run perfectly again. It ran for about 15 minutes and then froze. I was able to move the cursor (color wheel) around but the programs would not open or close. Next time I would boot the computer up, it would go to the folder with a question in the middle. This cycle has been occurring for two days now. I believe it is not the hard drive, but the cable connecting it to the motherboard. Any suggestions?