its ok now guys i typed in -dxlevel90 nad its sortedFirst can you give us a rundown of your hardware and any overclocking you may have applied.
Secondly, you tried re-installing, was that by deleting the local content and re-downloading from steam? If not then perhaps you can verify the integrity of the local game cache by right clicking the icon->properties->local files->verifiy integrity of local games cache.
You could also try defragging the games cache. I find a mixture of these normally solve my Steam games problems.
sounds like youve changed your resolution that your monitor doesnt support and reloaded the game.
Go to Steam
Select Games Tab
Right click TF2 > properties
Set launch options
Type in "-height #### -width ####"
Without the quotes and with your monitors screen resolution.