You might have a calibration problem with your throttle axis. Do me a favor: Start up AH, go offline, select a field. Choose a B-17 and 25% fuel in the hangar, and any bombload.
Spawn on the runway and start engines (hit E). Don't switch around selecting different engnies, leave it to all (shift E I believe selects all, but it also defaults to this selection).
Run full throttle. Jam it forward. Then bring up the clipboard. Choose "E6B" on the clipboard. Note the manifold and RPM for the highest rating listed on the E6B. Check the instruments in the cockpit. See if the engines are really at full power.
If they ARE, you might have a brakes issues.
If they are NOT, then you have a calibration issue.
If the instruments are a fraction of what the E6B lists, exist the game. Go to Windows control panel, Game Controllers, bring up your joystick and calibrate it. Do so deliberately and carefully. Make sure all the motions of the stick work when you are done (move them to their full extents and make sure the images on the screen match your input). THEN go into AH offline, and choose the Setup > calibrate joystick (or wherever it's located) and calibrate all the 4 axis and click okay. Try to take off in a bomber again.
If it's a BRAKES problem then you have something locking your brakes. Spacebar, C, and V, are the brakes keys. Make sure none are sticking. Also check to see if you have any part of your joystick mapped to work as brakes (Or perhaps toe buttons on your rudder pedals?). Find what, if anything, is mapped to the brakes.