My trailblazer starts just fine but after it starts if i hit the brakes or turn on the heat or try to let the window down the dash gets power, but no accessories work and the key wont come out

SOURCE: When brakes hit, lights flicker & loose accesories (wipers, etc)

posabilatey a bad earth

SOURCE: key stuck in ignition of Trailblazer.

There is a small 1/4'' oblong cover plate on the underside of the stearing column. Pop this out and there is a button you push in ( like the Crysler key relase) and this will allow you to remove the key.

SOURCE: 2002 trailblazer won't turn over or start

Check the cable connections at the battery and the starter for corrosion.
You may want to use a volt meter ( DC Volts ) for a more accurate reading.
Put the black lead on the battery NEG.,next ( with the meter on ) touch the POS. post/bolt with the red lead and see if you have atleast 11.0 volts, if so, try to bare a bit of the rubber insulation at the battery end and recheck with the red lead. Sometimes the solder weakens which causes a loss of voltage/current.
If reading is still close to or above 11.0 volts, next touch the red lead to the large post on the starter and see what the reading is,if this is still above the 11.0 volts,,,, check the fusable links located near the starter, you must have the same reading on both sides of the fuse ( round black plastic ).

SOURCE: 2006 chevy trailblazer will not start/turn over,

Sounds like the starter is the culprit,when the brushes in it are almost gone they will work intermittently and if the brushes aren't touching then you won't even get a click because of the lack of ground for the pull in portion of the starter solenoid winds.The next time it won't start,give the starter a tap or two to confirm this.It should start if i'm right.The starter is under the passengers side just to the rear of the front tire,bolted to the bell housing.

SOURCE: car wont start when turn the key for sometimes 20 tries

Manual transmission you need to step on the clutch. Auto you need to step on the brakes.