My Touch 4g turning off then drains battery

[Ashley Maggie]

Okay so I purchased a 16GB memory card for this phone and since then it turns off, I power it back on, then the battery is dead. I plug it in, then it either charges or it goes back to where the battery was before it turned off. I did the HTC update last year and it started powering off and turning back on again, like rebooting all the time. I had some kid apps that I thought was the problem, so I went back to the factory default, the phone still turns off. I cannot even make a post on Facebook without it turning off, but if i leave it alone on the charger, it last longer, but eventually still turns off. $200 down the drain! I need this phone for my online classes....Please HELP!!