How can i do a system restore without getting into windows?

My computer cannot get into windows and it says that bootmgr was not found. I deleted some hotkeys that were run when the system was restarted such as C:\config.sys and other .bat keys. Can I restore my laptop to an earlier point using the bios settings or the diagnostics? I have a dell laptop with vista. The diagnostics says that no errors were found but it cannot run the windows