Oblivion not starting is almost always a registry issue.

When you have Oblivion uninstalled run something like CCleaner to wipe out the registry entries.

Once that is done which will take a couple of minutes then you can reinstall and should have much better luck.

The better option is to launch Oblivion through a mod launcher, I like to use Wrye bash.

I'm usually reluctant to do regedit or third-party programs for that kind of stuff. I also try to keep my drivers updated, but have a unique setup that sometimes causes issues.

I was using OBMM, since I couldn't activate any plug-ins through the launcher, but since OBSE wouldn't launch either, some mods weren't going to work at all.

In the end I got it working, and it actually was a bit nostalgic since Oblivion was the game that got me to move to PC and I had no idea how to mod it but jumped right in. Reminded me of the days and days I would spend tweaking and checking, launch the game for 30 seconds to see if it runs, then quit and start tweaking again.

Anyway, if it helps anyone else, it turned out my issue was directly due to multiple installs in the past. And I had a similar problem with a couple other games before. For me there was simply a hidden folder in the AppData/Local/ directory with the old settings and hardware config. Deleting that whole folder made the launcher work fine, now I just have to convince myself to play instead of modding forever.

Interesting - there is always something new to learn, even after so many years of playing Oblivion. I wasn't aware that an Oblivion folder exists in appdata\local. I'm not surprised that inconsistencies between the current Oblivion configuration and the contents of this folder can cause crashes during the launch process.
Whoever suffers from such crashes should make sure to have a look at this folder.
To whatsnottaken: Deleting this folder fixed the problem for you. Was it recreated by the successful launch?

The folder was replaced, but now only has a couple text files listing the installed DLC. The old one had some Construction Set settings too, but I haven't launched that so far. I actually still have it installed from disk, but never play because I can't be bothered to pull out the disc anymore. So it's possible deleting that screwed my other version up too. :P

I mentioned I had a similar problem before, I believe it was after I re-installed the Witcher when I finished the Netflix series. Couldn't understand why it wouldn't launch when I certainly exceeded the requirements. Then found an old folder with the settings from my previous GPU, deleted that and viola!

Thanks. I just did a quick search for "oblviion appdata", and a few links were returned, for example, a general one in uesp.net, and a few more related with modding and configuring Oblivion (just in case you want to look into this issue further).

Hello! I'm more than 3 years late to the party! I had this exact same problem and spent the last 2 days trying to fix it. You may have seen people suggesting going to "Documents > My games > Oblivion" and deleting all the files there to get rid of any old save files and to reset and altered .ini files. This was the solution that worked for me. However! GOG and Steam have cloud sync features, meaning every time you delete those files to get rid of old saves, Steam and GOG immediately sync them back to the same place from the cloud. You first need to change settings in GOG Galaxy/Steam to turn off cloud sync, then delete all the files in "Documents > My games > Oblivion", then try to re launch the game. For me, GOG ended doing a complete reinstall to repair the files I had deleted, but this time it did not automatically sync my old save files.

the gog launcher has cloud save features so make sure you turn of cloud sync/save

This is the solution that finally worked for me. After that I could re-run the launcher and configure video settings and everything worked properly.

... means you had changed one or several ini settings earlier. There is always a risk associated with this kind of manipulation, and it's highly recommended to save the ini before editing it.