operating system not found in windows 7
Hi, I am desperate for help. I recently finished an internship where a colleague gave me a desktop computer he didn't want anymore. It was working fine but then the burner started to go so I went and bought a new DVD burner and installed it. The new one gave me nothing but trouble so I decided to take it back. I uninstalled all the software it came with and took it out. I restarted the computer and it ran a little slow but it ran. I shut it down properly and later wanted to get something off the hard drive. When I booted it up it said operating system not found. I don't know what to do? I or the person that gave it to me doesn't have any recovery or installation disks. I tried shouting it down, unplugged it and even hooked back up the new and old DVD burners and nothing changes. Can someone please give me detailed instructions on how to get it running again? I'm very desperate and frustrated! Thanks.