Usb connection malfunction
Some PCs may not recognize the Galaxy devices; if by PC you mean Windows, you can install the USB drivers by installing Samsung Kies.

One possibility is to try different USB ports, but since you have tried other PCs this seems less likely.

If the drivers are installed, the cable is the next likely culprit. Some cables are only for charging. You could borrow one to try, but data-transfer cables are cheap.

http://forums.androidcentral.com/samsung-galaxy-tab-2/302789-samsung-galaxy-tab-2-7-0-usb-device-not-recognized.html

http://forum.xda-developers.com/showthread.php?t=1861433