I had this problem, check a few things first is Hardware textureing on ? If it is try resetting to defaults. Open your Prefs folder. I don't know what it is on a PC but here is my Mac path I hope it helps. Home / Library / Preferences / Alias / Maya / 7.0 (depending on which version) / and throw away the prefs folder. Restart Maya and select the replace prefs whith new prefs. Let me know if that works.