Evo 4g won't read my sd card

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http://androidforums.com – I have an 8-gig SanDisk card in my phone, it contains half of my apps, hundreds of pictures, and just under 500 music tracks.I've had the phone and card for about a year and never had a problem.one day, I got in the car after school and an error appeared on my screen saying "sd card unmounted." I took out the battery and sd card, put them both back in and I was fine... For a couple hours.now no matter how much I try, it doesn't read it. I tried going in my settings to fix it but if I do it that way I'll lose everything; not gonna happen. Please help me (General)