sti4life

I have a f700bt and the unit powers on but there is no splash screen after 20 seconds the buttons go dim but the fan is still working...When i try to get into the service mode nothing happens on the screen but the buttons start to flash and then after a while they go dim..is there a reason i can not get into service mode i do everything correct holding the reset, eject, menu and map buttons. Thank you for any help

i followed this thread viewtopic.php?f=33&t=25465 .............and now my unit will start up with a blank screen and when i press menu i get to the menu but now of the buttons on it work except destination when i press destination the unit goes to the next screen and freezes also it is turning on and off every 3mins.....what do i need to do to get the unit to fully boot up and work.....prior to this problem i was in the service menu and pressed format mbr and the unit would boot up and shut off right away

How long does it take for the SDMLC image to write mine has been on for 40mins with the hour glass spining and it says reading image? i have the f700bt