Daniel's Thinkpad runs Windows XP and is experiencing the blue screen of death, or BSoD for short. Daniel can use the original install discs and go into recovery mode. That can fix anything that is going wrong. That will run the Windows System File Checker and replace any system files that are damaged. But it may also be a hard drive that is starting to fail. It would be a good idea to replace the hard drive. Luckily, it's easy to do with that Thinkpad.
Leo also says, however, that XP isn't being supported by Microsoft anymore, so it's high time to install a new OS on his computer. He recommends going with Linux. Xubuntu is a lightweight version designed for older, smaller machines. And check out Thinkpad Reddit for tips on how to keep that machine going.