Was there a patch? THis is so annoying.
btw i'm on PC
Processor: AMD Athlon? II Dual-Core M300 2.0 GHz
Ram: 4gb (3.75 usable)
Display adapter (graphics card i think?): AMD M880G with ATI Mobility Radeon HD 4200
System type: 64 bit
Edit: System specs

I belive this isn't a bug but more related to your gfx-card and/or it's drivers/settings?
I could be wrong though

Please post your system specs, driver versions, etc.

It happens to me every now and then, restarting my game fixes it though.

my specs are now at the top

no this has been from the day i got the game onward

Yeah, I remember getting something like this every time I tab out of the game, spells become invisible and water gets transparent, etc.
Only fix was to restart the game.

Driver version for that Radeon?

I am nearly sure i managed to get dx9 on it.

I guess you should make sure your drivers are up to date. I've had ATI Catalyst updates a few times since release. I think that includes the graphics drivers (sorry, not a computer pro)

Don't know if this is good or bad, but doesn't Steam have an option for updating ATI cards' drivers? I usually just do it when Catalyst says there is one.

Use the ENB Patch.

It's due to your weak GPU.

(My error about the question.) " Totally unnecessary. " (I'd missed the original emptiness of the OP on specs.) The PC in question (turned out to be) lacking any usable video solution, and must be replaced, entirely, or upgraded (only if it's a desktop, and I didn't care enough to find out that aspect).

Skyrim Minimum Requirements

* Direct X 9 compliant video card with 512 MB of RAM (and
sufficient performance to actually put that VRAM to use)

The HD 4200 is only an 0nboard video chip with Zero VRAM.

Just another 'gaming' laptop with anaemic gpu specs below posted minimums, and its owner wondering why the graphics aren't working perfectly.