Overheat is the number one cost of hard drive failure.

The best solution is with a case fan.

I bought the SilenX Case Fan. It advertised high air moving capacity with low noise. Did it live up to it's reputation? you bet!

The other solutions is try to unclog the internals of your case. Put your cables asides and see if there's any space for the air flow. If all failed, then you would need to bush some fans specially designed for hard drive cooling. Those are not very expensive and certainly a cheaper than losing your data.