In order to solve the issue, press Windows + Pause/Break key combination and open Device Manager. Expand the Universal Serial Bus controllers list, right-click on the driver and select Uninstall. After that, reboot your PC, connect the device and press Scan for hardware changes icon from Device Manager. Select Mass Storage from your Xolo X900 display and check if it works. If not, go to your device Settings, select Backup & Reset, perform a factory reset and try again. This should fix it.