invisable/flickering graphics in gmod

This is the very first time I have had this problem. My problem is that the spawn menu backround is sometimes disappearing and then reappearing! Another problem I have had is the blood effects are squares/boxes with a line going across it! Heres an image:

http://img189.imageshack.us/img189/5386/gmflatgrass0000c.jpg

and last: The box around the health meter at the bottom left of the screen is disappearing/flickering at random times! Could someone help me?