My Ti 89 won't turn on an I put brand new batteries in

TI calculators have a habit of dimming the screen contrast when the batteries are changed so that it appears as if the calculator isn't turning on. Turn the calculator on (or at least press the ON key). Press and hold the diamond key and press the the + key to darken the screen. If you go too far, use the diamond and - keys to lighten the screen.

If this doesn't do it, please reply to this post and we can try more drastic measures, though they may cause the loss of memory.

Get a specialty screwdriver called a Torx, with a torx 8 bit and remove the 6 screws on the back, slide a credit card between the slit down the middle of the sides of the device to divide it into the front and back half, the back half (that has the spring battery contacts) are touching the main board on the front half through these copper square battery contacts near the bottom of the front half on the inside. Chances are the copper from the main board where the spring metal touches the contact is scratched and flaked away leaving no connection in the circuit, slightly bend the battery contacts to the left or the right so they are in contact with fresh copper and reassemble! I got a lot of H.W. to go through and this sight would have had me erase ram cache, reinstall firmware, buy new main batteries, main backup batteries, and the buy a whole new unit. No one here thought to think to check with a voltmeter and its a shame, theres such disinformation on the net. And to those who write "buy a new one", get a life and stop being useless to world.