To fix/install Android USB driver on Windows 7/8 32bit/64bit:
- Connect your Android-powered device to your computer's USB port.
- Right-click on Computer from your desktop or Windows Explorer, and
select Manage.
- Select Devices in the left pane.
- Locate and expand Other device in the right pane.
- Right-click the device name (Nexus 7 / Nexus 5 / Nexus 4) and select Update
Driver Software. This will launch the Hardware Update Wizard.
- Select Browse my computer for driver software and click Next.
- Click Browse and locate the USB driver folder. (The Google USB
Driver is located in
<sdk>\extras\google\usb_driver\
.)
- Click Next to install the driver.
If it still doesn't work try changing from MTP to PTP.