Possibly fried CPU

I apologize if this is the wrong place for this as I was unable to locate anywhere that seemed more appropriate. My friend has been having an issue with his processor for the last year or so, and has finally decided to get back into PC gaming so I've come here seeking assistance. His processor is an Intel i5-760, and it has been sporadically dropping to 0% CPU usage for 5-10 seconds and then returning to normal for a random amount of time between 1-5 minutes. This problem was bad enough to make games completely unplayable. 

We're fairly certain that the cause of this issue was the computer falling onto its side due to his brother tripping over a cord plugged into the front panel USB on his case. We believe the problem is either with the CPU itself or the motherboard in some way, though its possible its something completely different as our knowledge is somewhat limited. As the budget is tight for replacement, we're hoping to narrow it down as to avoid wasting money on an unnecessary part. Any advice on how to figure out exactly where the issue is would be greatly appreciated. 

Is the CPU fan running? If not, thats the problem.

Otherwise, try the hard drive. Sounds like a hard drive error.

He says the CPU fan was running and temps were fine. Now a hard drive problem I had not even considered, that's very surprising. If I may ask, what exactly about the hard drive would cause such an issue?

Tipping the PC over could have damaged the Spinning disk inside of it. When the HDD is being read, if theres an error, it can lock up for a second, causing the drops in performance to 0%, and making games unplayable.

Wow, haha it's been about a year and he never considered that, but that makes a lot of sense and I'm frankly embarrassed to have missed it. I appreciate your advice, and we'll definitely try swapping his hard drive with one he has lying around to be sure. Thanks again!

to me it sounds like a psu issue