Check the tightness of the connection of the usb cable with phone and computer. Make sure the cable has no abrasions or kinks. If the computer doesn't see the phone once connected, try connecting the cable to a different usb port on your computer. Wait some time so that the system determined the device is connected and configured it properly.
See if the icon for new hardware found in the taskbar. Quite often, the computer does not see phone new models, and their definitions, you must install the appropriate drivers. If the kit supplied boot disk, place it in the CD drive and run the installer. When there is no disc to click with the right mouse button on the icon "My computer" and select "Properties". Go to "device Manager" and look for an unknown device with a yellow exclamation mark. Click on it and select "Install driver". Specify as designated drivers search the Internet and wait for a while until the system detects and installs the necessary services.
When you connect some phone models the discovery process the new device will not start. Just try to go to "My computer" and see if there are any in this folder a new icon removable devices. Click on it and you will be redirected to the contents of the memory card of the phone.
Please note that when connecting to computer iPhone latest version you also need to click on the screen of the phone and remove the block. After that, the device screen will be prompted "Trust this computer?". Select "Yes" and only after that folder the phone will be available in "My computer".
Disable temporarily the antivirus system and other processes consuming a large amount of resources, if the computer doesn't see the phone. Outdated equipment and "clutter" of the operating system can slow down the detection of new devices. Also try restarting the computer and cell phone, and then reconnect the device. The cause of the problem can be various internal software failures, and eliminates rebooting.