For situations like that, I have a "rescue CD" running the Knoppix
distribution ... which is a complete Linux distro that runs entirely on a CD-ROM.
When my computer was in perfectly good working order, I booted up Knoppix and took the time to really learn how to use it. It has proved to be priceless, not only for debugging botched Linux
installs, but for botched Windows
On another computer, go to the Knoppix web-site, grab a CD-image and burn it to a CD. Boot that CD. This will eventually take you to a functional Linux installation that is not dependent
on whatever your hard-drive contains; "borked" or not, Linux or not.