S.M.A.R.T errors can't install OS X Mountain Lion

I tried to download OS X Mountain Lion but all I get is a message reading .......... This disk has S.M.A.R.T errors. This disk has a hardware problem that can't be repaired. So what is a S.M.A.R.T error ? Can it really not be reparied ? What shall I do now ? No sence in paying $19.99 if I can't use it.

Thanks for any and all help