I tried to watch MLB.tv and it wouldn't work so i did and update and restart... and now it is stuck in repeated restart mode... it tries to restart, shuts down, tries to restart...
Ultra model. I pulling the power cord for a few minutes but got the same when I plugged it back in.

Does it have an SD card installed? If so, remove it and try the startup.

Also, is this your only Roku? If you have another device, use the other device to remove MLB.tv from the account (highlight the app, Options > Remove). This would be in case there's a bug in that app that's causing the problem.