Texture issues across all games VERY ANNOYING !!!

This is a problem I've been struggled with for over a year. My HD5870 will work perfect for months then it randomly starts causing trouble. Random lag spikes in games, bad texture sampling across ALL games (textures look N64 blurry, VERY ugly). My friend told me he had this happen to him once but ran Malwarebytes and that fixed the problem for him. Not for me... I just got Skyrim and this problem makes the graphics so ugly even on High.

AMD Phenom II X4 3.4GHz
ASUS HD5870
4GB DDR3

Any ideas? I'm about to throw my PC off the window... BF3, Skyrim, Bad Company 2 are all unplayable...