This is not a Dell hardware  problem.  The Applications Software section may be the best place to post on the Dell forum.  However, you should be contacting Yahoo first.   Keep in mind, the PC does not have to be compatible with Yahoo.  Yahoo has to be compatible with whatever it's being used with.
I have newly bought a Dell desktop Vostro 460 with Chinese Windows7 professional 32-bit OS, I have installed Chinese Yahoo Messenger 11 but thevoice & video button grey out that I cannot start these functions. However,I can invite other to view my webcam and view other's webcam functionallythrough Yahoo Messenger. Also, my webcam and mic work normally through QQ. Do Dell board the functions of Yahoo Messenger? Please help me to solve the problem.   
Yahoo Messenger 11 voice & video button grey out