Booting from a repair disc, while it doesn't have the option to boot to Safe Mode, has the option to boot to the command prompt. From the command prompt you can do several things. For one you can copy any data you want to save to a flash drive using the XCOPY command. You can type XCOPY /? if you need to know the syntax. You can also do a check for corrupt system files by issuing the following command: sfc /scannow.
Good luck.