No display on monitor Power not on Switch on at power point and monitor. Also check that the computer is on and the monitor cable is firmly plugged in the correct way. If you computer is an old XT, it should be set to that. Try changing to the other mode and reboot the computer. Pugged into the incorrect port Mice plug into serial ports.
Most computers have two serial ports so try each one.
On the bottom of the mose is the ball. This can become very dirty and transfer dirt on to the rollers in the mouse. If it is a dot-matrix printer, replace the ribbon. If it is an ink-jet printer, clean the print head or replace the ink cartridge. If is is a laser printer, remove the toner cartridge and shake it up.