fix a small rollove problem

Hello, I got a small problem for my web site ([login to view URL]). Whenever I rollover the mouse on the four menu on the top right corner (About CoCo, GemStone, Shopping, and FAQ). The menu was gone and become background. If you take a look at the site, you will understand. If anyone would like to try, I will give you the access to the site. The pay is $20. Thank you!