All games are cleaned and tested on original systems before shipping them to you. If you're using an emulation system, like a Retron 5, some games will not be compatible, we try to list these incompatibilities on the product page so you are aware before checkout. If it is compatible or you are using an original cartridge system please try cleaning the contacts. This can be done by applying 99% rubbing alcohol to one end of a Qtip and rub it along the contacts of the cartridge. You can then use the dry end of the Qtip and rub it on the contacts again. If the Qtip appears dirty then select another Qtip and repeat the process until there is no more dirt/dust. This will more often than not fix the problem.
If you are having problems with a disk based (CD, DVD, or Blu-Ray) game gently wipe the game with a damp, soft (lint free if possible) cloth. Be sure to wipe from the inside of the disk to the outside. This will clean off any dirt, fingerprints, etc that may be causing issues.