something very similar happened to me
Last night i reformatted my xbox 40gb hard drive with slayer's autoinstaller 2.5. Then i put some game backups on the hard drive and everything was working fine. Next, i put some videos on the hard drive, but alas the videos looked like they were too skinny so i enabled stretch and everything was fine. Then i added some more videos went looking around in the new dashboard (evox v+3921 from slayer's autoinstaller 2.5). I don't remember everything i did, because I was a little sauced, but i'm pretty sure i didn't do anything too retarded.
***note to self - drinking and xbox modifying don't mix
After a reboot, i could hear the startup sound, but there was no video. When i turn the chip off (i've got xecuter 2.2 lite), still no video. All cables are good. Sound, but no video on the boot.
When it boots from the chip, every 20 seconds or so, the screen flashes and just after that the dvd drive whirls a bit and the hard drive chugs slightly. When i try to open the dvd drive, it opens fine, but when the screen flashes the dvd drive closes like it's rebooting, but no frag or anything. The dash isn't working, cuz i can't get a connection through ftp.
Problem with connections? Nope, double checked all connections and even tried different a/v setups.
Problem with dashboard? Maybe, but then why can't i see anything when the chip is turned off?
It might have something to do with NTSC or PAL settings, but what's the deal with the screen flicker and drive spinning? Also, if it was JUST a NTSC or PAL thing then the dash would boot and i could access it from ftp.
So, needless to say, this is quite frustrating, and i haven't found any similar problems on the forums.
If you've got any suggestions or have any idea what's going on, I could use all the help i can get.
Thanks!