I believe my macbook pro hard drive is bad. I erased the drive and reinstalled the OS and the macbook still runs really slow. I dont know if the hard drive is the issue.

Question

I believe my macbook pro hard drive is bad.  I erased the drive and reinstalled the OS and the macbook still runs really slow.  I dont know if the hard drive is the issue.

Answer 1

Did you try an SMC reset too? It's easily done and none of those resets to the best of my knowledge hurt anything. When I was fooling with my system, which at one point was a home made Fusion setup, I needed to reset the SMC sometimes to get the drives recognized. Reading the documentation the sudden motion sensor is drive related but that seems to be about it.
Some more specifics may be needed about the drive itself, the model number of your unit, and the OS version you're running.
At present, the problem seems sort of odd to me. FWIW cable problems can be quite intermittent. I used Scannerz to find some of the problems on my original system that I later converted to a new HD and SSD combo. It can find lots of problems if you learn how to use it right (HD problems, logic board system faults, and cable problems) but you need to get a system at least partially up and running to use it, and it doesn't sound to me like your there right now (in other words, don't go out and buy it because at this point I don't know how it could help you)
Another word of advice would be to not go out and start throwing parts at a problem unless you have a good idea what the source of the problem is. If you have a logic board problem, new drives and new cables won't make it go away, you'll just be wasting your money. Logic board problems, cable problems, and drive problems can all have very similar end user symptoms. The article that I linked above named "Hard Drive Problems" has a section on general symptoms of problems and if you read the article it becomes clear there's a lot of overlap associated with different types of problems.
I assume that your unit isn't under warranty. If, by chance it is I wouldn't even fool with it and I'd take it to Apple and let them deal with the problem. You also might want to check with whatever Apple sources you have available to test your system, like an Apple store, and see how much they'll charge (if anything) to evaluate the system.
I certainly hope this helps.