My monitor keeps freezing when I play games and it says "Sync out of range". What could be causing this error. I have already adjusted the refresh rate, but that only worked for a day or two. Is it a graphics card or monitor issue?

What monitor are you using, are you using specific drivers for your monitor? what resolution and refresh rates are you trying to run? what games are you running? what do you mean when you say you adjusted the refresh rate where did you do this?  a little more information will help.

Does the error appear only when you play games? if yes, then either your in game resolution is set higher than you monitor can handle.  Otherwise if it might be a result of your video card going bad. This is error when the monitor either gets no output from video card or a signal it can't handle. Some bad drivers can cause the graphics card to alter the horizontal sync randomly giving this error. Try different drivers. Again overclocking the card sometimes leads to this error, try stock values or even see if underclocking works.

Bootup in safe mode and uninstall your video drivers.  
 
If your games are the issue... then reinstall the game.. it should put the resolutions back to default.