So, I started to play Skyrim again after not playing for quite some time and, to my suprise, I found that I'm getting about 23-26FPS all the time..before, I've been playing Skyrim on Very High with 50-60FPS. I've tried disabling all my mods (no difference in FPS), playing with the graphics settings (no difference). I'd rather avoid doing a complete reinstall, because I have slow internet and it'll take a long time to redownload, but if I have to I will.

Any help? Really weird and annoying. D:

Have you tried updating your GPU drivers? There may have been some Bethesda patches since you last played, and a driver update may be required.

Secondly, I know you said you played with graphics settings, but it might be worth double checking the shadows. They can be a performance killer on mid-range setups (and even high-end, to an extent). Set them on low and see if it helps at all

GPU drivers are fully updated, and tried setting shadows to low, and no dice.

Anything more suggestions?

Two more:

1) Try starting a new game, in case the low FPS is somehow tied to your save files.

2) Disable all mods, and start a new game.

If it's still low after that, you could try deleting your SkyrimPrefs.ini file and allowing the game to create a new one, and see if that fixes the problem. Otherwise... I'd suggest a re-install

EDIT: Before re-installing, right click Skyrim in your Steam library, select properties, click the local files tab, and then click "verify integrity of game cache". See if Steam finds something critical missing from your install.

EDIT 2: (lol) Also might be worth checking Nvidia Inspector or Nvidia Control Panel and checking that you haven't somehow got the game playing with super sampling or something crazy like that. Those programs will save those settings. It's unlikely, but maybe you turned it on once out of curiosity and forgot about it. Revert the Nvidia settings to default for Skyrim if they aren't already