It will most likely need a bunch of capacitors replaced and/or solder joints redone.
If you search the forum, you will find a lot of similar cases, like these:
http://forum.beoworld.org/forums/t/14781.aspx
http://forum.beoworld.org/forums/t/12167.aspx
...and an excellent repair workshop on the preceding models, which have much in common with your MX7000:
http://forum.beoworld.org/forums/t/10557.aspx
As the red standby light still comes on, the power supply is still partly working and there probably isn't that much damage. But stop playing with it until it has been looked at, it won't repair itself and it will eventually end in smoke.
Regarding this problem, MX4000/6000/7000 and LX6000 are all just about the same internally.