Linux live disc. If it's FAT32 you can read the shit in Linux, and IIRC there is Linux software that will read NTFS partitions, then copy what you want to keep to an external.
Or use partition software to create a new partition, assuming there's space, install a fresh copy of Windows, copy what files you want, and blast the old partition.
Or mount the harddrive on another computer and copy the files you want before wiping.
In both cases would not suggest running any executables and you should scan anything from the old installation before opening it.
Or do a network boot of an image.
Or reformat and start fresh if there's nothing worth saving. This is the easiest solution, because I'm sure you have scheduled backups of anything you want to keep to an external location LOL