Replying to Having issues with my t2i

alright so i went to turn it on this morning, it said the card was not compatible or something, change card. so i did, wouldnt even turn on. tried formattig the first card in camera, wouldnt, reformatted them both on the computer with some software i downloaded, wouldnt work. i even bought a new card, wouldnt turn on with that either. i have ml installed but its been working great for the past few weeks, and my two first cards have also been working just fine. any help? thanks