I have a V1.4 of V1.5 with Focus chip, TSOP'ed with Raincoat and 4981 and it worked like a charm for a few days, as they always work perfect!

Now, after I turn this xbox on, I see the Xbox logo, get to the Xecuter2 logo, then reboots, reboots, and so on all the time.

Mounting a Duo/X2 chip doesn't fix the problem. Installing different IDE cable, different DVD-rom drive, different HD's (all unlocked), still nothing works.

But I can still "boot" or "startup" to the Xecuter2 bios. Then it pauses shortly, and reboots again.

Does anyone have an idea what I can de to get this box running again?

will it boot from a DVD?

You used a bad TSOP image.

http://www.llamma.com/xbox/Repairs/eeprom_fix.htm

That should help you fix it

No,
Xbox won't boot from DVD, I'll try with a DUO/X2 the Eeprom fix repair to see if that works.