iphone 3g running 4.0.1 will not go into DFU mode

Alright guys. I've put many iPhones and iPods into DFU mode in the past. I KNOW how to do it so if you came here to say,
"
1) Open iTunes
2) Power off your iPhone
3) Hold down the power and home button for exactly 10 seconds
4) Release the power button and continue to hold the home button for 30 seconds or until iTunes recognizes it in recovery mode
"
you're wasting your time. I've done it before. Multiple times. When I do this, it looks like it's going to enter recovery mode, but then goes back to the no sim card page, as if it's ignoring the button sequence. (I'm looking to hacktivate with my jailbreak) Is there a patch that I don't have or some pc software that I can use to force DFU mode? Thanks guys

 

I just tried doing it without being plugged into the computer. The apple boot screen won't stay on long enough to last the 10 seconds. It gets to about 7 and the phone shuts off. Also, it's a 3G.

Reaction to expected suggestion: I tried releasing the power button when the boot screen appeared, but before it shut off at 7 seconds. After continuing to hold down the home button, the iPhone flashed the recovery screen, then returned to the no sim screen (like it does when plugged into the computer).

 

Yea it's 4.0.1. I just SHSH blob restored it about a half hour ago.

 

Also, here's the goal for the phone. I'm going to limera1n to jailbreak/hacktivate it on 4.0.1, then use iREB and sn0wbreeze to update to 4.1 so that I can still unlock it with ultrasn0w. For any of this to happen, though, I need to be able to enter DFU mode.