I've been trying for the past hour and a half to get this fixed. I've sifted through other topics, faqs, and whatnot and cannot find the answer.

The problem started after I finally got around to installing some mods. I think the problem may be coming from the Unofficial Oblivion Patch, though I'm not sure. I can't for the life of me figure out an easy way to uninstall it and I spent a quantity of time trying to just delete the individual files, to no avail. I am now trying to reinstall Oblivion.

Can anyone help me with this?

If I were you, I would post this over in the mod section along with your mod list. I'm darned near willing to bet you did not install a mod properly or it's not in the correct load order. I have the UOP plus 100 other different mods and never had this issue. Unless you are pushing your PC to the max overload limit for what it can run.

A few questions. Did you back up your original data folder as is called for before you installed any mods? Also, did you read each mods readme and uninstall according to their directions?

If you are using screeneffects.esp (OBGE plugin), there are some circumstances where it will default to weird values (never did solve the issue myself). If you are able to go into the menus, go to the screen effects controls and click "Reset" or "Default", would always work for me.

If iremember correctly i once had a problem like this. I had an older graphics card and i installed a mod that used shader model 2.0, which my card didnt support, resulting in the grey screen. I cant remember but hdr lighting may use 2.0 as well, so you might want to try disabling that.