If you've downloaded and installed items you may have corrupted the driver(s) for the cursor. Try this: Go to Control Panel then Add New Hardware. This will scan your computer to see if there is any hardware that is connected but for which there are no drivers. Your Operating System (OS) should find current drivers since the system was working prior to its failure...
Additionally, if you're using WiFi for internet connectivity, simply unplug the WiFi modem for a few seconds and the reconnect...