TuffTEST program results

I'm trying to figure out what kind of hardware problem I'm having. When I run the licenced TuffTEST program everthing passes until I reach the "fixed disks" test, at this point hundreds of "errors" come up and a message saying "error log is full" appears. The error code is F004. When I get to "fixed disk 1" the error code is F101. When I do just the "extended memory test" (I have 1024mb ram installed) everything is fine on the first 2 passes, on the 3rd pass the 960-1024mb sector "fails". On the 4th pass all sectors pass but when it reaches 960-1024mb it just hangs on "testing". I can't find out what the error codes mean as the TuffTEST website is down, and I bought new memory and get the same results, so I presume the memory is not the problem. Does anyone have any idea what kind of hardware problem I have? Aside from this, the computer seems to operate fine.
Thanks for your help.