did the games work before?have you got restore points going back as far as two months you can restore to when all was well?
do you have direct x9? most new games need this to run correctly.
if you do have it,also check your graphics card drivers are direct x9 compliant up to date as well.
also check in: start/control panel/performance and maintenance/administrative tools/event viewer
look under the system and application tabs for any errors that may help pin point the problem.
also try cleaning the disc/s and cd drive lens with a little isopropanol(get it from chemists)