Try reinstalling the usb drivers or use a different cable. Make sure you reboot after driver installation. Also, connect the phone with pc and go to device manager and see if it appears there. if it has a yellow triangle in the device manager then you need to update the driver.
Edit: when you connect your phone, does it start charging? because if that is not the case then your phone`s usb port might be damaged
1. Nokia 1100 (first phone-originally belonged to mom): retired
2. Nokia 2690: Retired (fell in water.. :P)
3. Samsung Galaxy Y GT-S5360: USB port burned... Still on Duty
4. Samsung Galaxy S2 GT-I9100: SOLD
5. HTC ONE X: Current Phone