A couple of months ago I installed windows 8 from 7. Now I want to get rid of it. Me being a dummy called Microsoft support. They said I need to back up my files. I told them I did not have the external hard drive space to do it. Anyway, Now I'm questioning this. I Have a fresh copy of windows 7 that can be used to install on my computer. If I install windows 7 what will happen? Will I lose all my data, will it replace over, or will my system crash and burn?

Now, presuming that a downgrade works in the same way as an upgrade (and I am in no way suggesting that it will), your old files and folders should be placed in a windows.old folder in your C:/ drive.

However, should something go wrong during the installation, you would likely need to reformat your hard drive and would thereby lose all your files.

I would highly recommend getting an external hard drive (they're pretty cheap these days) and doing a back-up of at least your personal files before attempting any OS installations.