How do I get rid of Ubuntu?

This is kind of a rhetorical question. I installed Ubuntu on a Dell Dimension 8300 running Win 7 with dual monitors about a year ago to explore Linux, primarily. I never got the e-mail to work right and put is aside. Recently, I returned to the project and after struggling with the calendar and e-mail functions, decided to upgrade to the 12.10 version (I think.) It failed to completely load. A package was missing as I reported earlier. Now the performance was distinctly bad but at least i could use the 2D graphics. However, I decided that the only way to recover was to upgrade further to the current version, 14.10 (32-bit). I attempted this using the ISO download. When run as a trial, it was incapable of properly handling the dual monitor configuration, which is no problem for Windows. I proceeded to install, but it insisted on installing to an external USB drive, rather than replace the existing installation. When I attempted to run it, it would only get so far as displaying a violet background screen with the Ubuntu logo and nothing further. it would flicker on mouse activity but nothing more.

So now I am dead in the water as far as Linux/Ubuntu is concerned. I do not think the installation is recoverable. I cannot simply delete files as they are invisible to the Windows system. I would still like a running installation but I cannot expect any of the past versions to replace what currently exists. How do i get rid of it? How do I recover? Must I format the drive in order to get back to normal? What went wrong?