short story: i successfully rooted my sensation last saturday night. i successfully installed android revolution hd 2.3.4 (the xe rom). worked flawlessy for 2 days, then random power off. two more random offs the next day then phone becomes completely and utterly useless. won't turn on, won't go into fastboot, won't respond to micro usb connection (yeah, fresh battery too, tried many ways to prompt boot, no luck). i am still under my warranty, so if i send it off can the techs tell whether or not it's been tampered with.. if it's just basically an empty shell?
If it won't turn, there's no way the tecns can tell if it's been messed with. I bricked my sensation once, just like yours, wouldn't turn or nothing. I took to a t-mobile store- still under warranty as well, they entered it it their system and I received another Sensation in the mail about 2-3 days later.