A disk read error occurred. Press CRTL + ALT + DEL to restart.

If this error was posted before I apologize. I tried searching for it on here but I couldn't find anything. So I get a text from my gf at home while I'm at work. The computer was displaying this screen. She was in another room when it happened. She came in and it was just randomly on this error screen. I've tried resetting the BIOS both by entering BIOS and saving to the default settings and by removing the CMOS battery. I've also put another harddrive in to see if it's the cable that's bad, but that's not it. It's an older computer so it's not that much of a loss other than the fact of it being the only computer we have right now. In a day or two I plan to purchase a used office computer from a company store. Hopefully having another tower will help me find the problem or at the very least I could swap out parts. But if anyone knows of some ways to fix this without another computer that'd be great. Also this computer's optical drive is stuck (the pinhole eject doesn't even work). But I know there is no disc in it.