..i can not start any web cam on my linux u.e. 2.7. ..why? i tried a lot of web cams,but i cant find the one...can you help me?

Usually with any device, esp. a wireless one, you have to plug it in with a USB for the first time. If your distro doesn't work with hardware it is easier to switch distros by testing live media with your hardware. Fighting with Linux when it doesn't like or see hardware is frustrating. Backup your /home directory. You might first try plugging in your webcam and then using yum or yumex to update while it is plugged in.

See if it's found...

I assume that this webcam is connected with USB.

If you boot linux, then open a terminal and use the command "dmesg", you will see what linux finds and loads when it boots. Try this without your webcam plugged into your system, then with, and look for any differences.

Otherwise, the suggestion about booting a newer version linux live-cd while the webcam is connected to see if it finds the webcam seems a good one. The webcam may not work, but you can use the terminal and the command "lsusb" and look for a listing of the webcam as a USB device. Then use this ID number to search the Internet for more information on its configuration.