If you can not add or select fixtures you've lost your light fixture profile. If the internal battery dies (small round battery like in a watch) and you turn power off you'll loose this profile. ULink (upload) new profile. Can find instructions on Elation support Downloads.
If the 260 cycles and does not load/boot up, then its a firmware issue.
If firmware is corrupt and 260 not responding:
Press and hold function buttons 1, 10, 20 and 24 and turn this unit on. Then send firmware file for the Magic 260 with the u-link. If you need firmware 1.04 (1.02) send message.