have you tried removing the mircosoft kernal from your launch menu then re-adding?
I currently have a box of a friend that does the exact same thing. You get nothing.......just a daunting blackness. From what I've read the problem appears to be a corrupt MS bios. A new copy your appropriate MS bios version can be flashed back to the TSOP but at this stage I'm yet to perform this myself. There are some guides on reflashing the TSOP in the tutes section. I have a similar thread posted here and from what I gather the '29 wire' TSOP flash method is what I'll need to use. You might like to have a browse through the TSOP forum here too.
Also, are you able to boot your MS dashboard ok from whatever dashboard you have installed. If so, that tells you that at least the files for the MS dash are ok.
Finally, as to other possible causes, I'm not 100% sure that its a corrupt TSOP and am actually wondering if a corrupt EEPROM might be the cause. What were you doing before the problem occurred? Did you notice anything wierd and have you ever had EEPROM troubles with your box in the past...