My Skyrim on PC isn't working right?

I can play it but at one point or another it just closes the game and when i click play again (this is on steam btw) it either says something about no being able to access Steam Cloud or not enough storage. but i have almost a terabyte of memory and I've checked how much I've used and it's far from a tb. I've also backed up the skyrim files i have onto my computer but it still does it. and at one point i changed the quality from low to medium and it didnt do it for a while. i also have about 40 mods on steam and maybe 3-5 mods from nexus but it didnt do this till about 5 days after got the mods. Whats the deal?