Ive been fighting with this problem for the last few hours. No matter what the settings are before hand (I play on high) the textures automatically revert to low res and it looks really bad. I havent reinstalled yet but I have moved and unchecked the Hi Res Packs, disabled all mods, deleted Skyrim.ini and reset it by verifying game cache. I really havent done anything that could goof with the textures beforehand. I dont have any shader or texture mods besides the hi res pack supplied by bethesda.

Windows 7 x64
ATI Radeon Mobility HD 3670
Intel Core 2 Duo 2.53 GHz CPU
4GB RAM

That's because your GPU is very weak. Your GPU isn't really capable of using them anyways. Low is about right for your hardware.

but ive been using high since 11.11.11. ive only recently run into this problem.

Dude your GPU only has 120 Processor cores on it, which also comes with a poor texture fill rate. You need a GPU with at least 640 Processor cores and 1.2+ GB of VRAM to be able to run this properly. (ATi)

You dont understand. I HAVE BEEN RUNNING SKYRIM ON HIGH SINCE LAUNCH WITH NO PROBLEMS UNTIL NOW. It doesnt matter how bad or outdated my card is if it works and plays the game on high. The textures were set on HIGH until I installed the Hi Res Pack when it was released. I have been using it ever since.This problem is very recent.

Im reinstalling right now. Hopefully that fixes the problem

The high rez texture pack is a higher rez than playing vanilla Skyrim on high.
Seriously, get a better card and then you'll see.

Fixed the problem with the textures by rolling back the drivers from v12.4 to v12.1