I'm at my wit's end here...
I got a Raspberry Pi 2 a few days ago and haven't been able to get it to run properly.
The most "stable" OS I have been able to get going is OpenELEC 5.0.8, which is installed on a Transcend Class 10 SD card (SD Formatter -> Win32Diskimager). It only boots up properly if there is no config.txt on the card, strange as that sounds.
Whenever the Pi is under load (few seconds of video, scrolling through menus too fast, etc.) it stops, the screen fades to black and a few seconds later the menu comes up again, but I can't do anything and I'm stuck in a reboot loop until I unplug the power.
I've also tried OSMC (NOOBS, Windows Installer and Win32DiskImager) and Retropie, but haven't been able to get them to boot up. OSMC only shows a frowny face and Retropie gives me frequent "Segmentation" errrors.
I really don't know what's going on here. I've tried various other SD cards (SanDisk, Toshiba) and all the wall plug PSUs and cables in the house, but nothing helped.