Every time I try to play 18 wos convoy I always get a box that says prism3d.exe not found can anybody help me I want to play this game?

Try downloading and installing updated drivers for your video card. If you have an nvidia card, you can get them from NVIDIA Drivers (http://www.nvidia.com/content/drivers/drivers.asp)
If you have an ATI card, you can get them from Drivers & Software (http://ati.amd.com/support/driver.html)
If you have any other type of card, you can post here and we will try to find a link to some drivers for you, or you can try the webpage of the manufacturer.

mine says 18 wos convoy with a red X before it