Removable drive stopped working

My step-daughter downloaded a questionable program, and installed it without running a virus check. Though I cannot say that caused the problem, the ‘A’ Drive stopped working soon after. I’ve run various system checks, all of which say the drive is functioning normally, and no viruses are present. I tried another drive from my old PC, which I know worked fine, and, lo and behold, that won’t read anything either. There are various other problems coming up too; programs lock or shut down on theirown, warning that system is overloaded comes up, though more than 60% resources are free. The list goes on. Please help me out here! I’m running Win 98se, with 20gb hard drive on a Pentium 111 500mhz.