Ipad 1 5.1.1 Apps Crashing even newly DFU Restoration. Please HELP.

i have my ipad 1 iOS 5.1.1 all apss crashing.. i tried to DFU restoration and didn't install any program but still my app store is crashing. i installed facebook crashing same as twitter. is there anyone there who have the same problem and solved it already?.. do i need to downgrade my iOS? if so whats the stable iOS for ipad 1? TIA