This is a known issue if you're using a USB mouse with the newest version of Parallels.
Right now, until Parallels releases a fix, the best solution is to shut down the VM, navigate to the configure menu for your virtual machine, then do the following:
- Click on the Hardware Tab
- Click on "Boot Order"
- Expand "Advanced Settings"
- Add the following to "Boot Flags": devices.usb.mouse=0
- Boot your VM and the problem should be resolved.