why wont .nds games work on my nintendo ds anymore?

i have downloaded many games from here and they have all worked, my cousin decided to download left 4 dead 2 on my computer and all of a sudden the save files had left 4 dead logo's on them when i pluged the r4 into the computer. i have left 4 dead and have tried to download pokemon, white, black and conquest. none have worked. they all come up untitled and a blank ds for its picture. does anyone know how to fix this :(

I'm not getting you.
Could you please post a screenshot of your problem.

That 'white screen' you get when trying to play the rom on your R4 with the NDS console.... its because your R4 firmware is outdated.
Go look around if you can use YSMENU/TTMENU/WOOD R4 as secondary firmware in your R4....again which to use depends on what R4 you have in hand. If you need assistance/recommendation on which to use, then you will need to post the exact same words you see on your R4 cartridge sticker/box, including the cart's website/picture. Otherwise we can't help you.