Gateway 2000

I recently had a Gateway 2000 Pentium II with a 233 MHz givin to me. The computer had WIN95 on it and problem is that the person tried to load WIN98 on it, it won’t load (I don’t why it won’t load) so they removed it. Now when you turn the machine on it gives you a POST and WIN95 starts then it goes to DOS. I tried to boot it with a WIN95 boot disk and I got this message: “OS load in process” Disk I/O error replace disk and press any key”. I want to try to fix this without taking it to a computer shop, but I don’t know where to start. I was hoping to get some help here?? Any help or ideas would be great……