I just Modded my first XBOX and had the same problem after flashing. Xbox would switch on, off, on and then green/red leds would flash with no video. XBOX would however boot to MS dashboard (i.e. Chip switched off) and I copuld ged to the backup BIOS (holding power + eject). I fashed the XBOX with "X3 3294.bin" as I have an Xectuter 3CE installed. I checked the BIOS folder on my PC and found amother BIOS "X3 3294 v16plus.bin" file in there, so reflashed the chip using this BIOS file instead. Voila, the XBOX booted first time without any probelms.
XBOX Details
XBOX Crystal V1.6
EXECUTER 3CE
Soldered installation
Hope this is some use.
XBOX Noobe