Finally I'm done. After I e-mailed you guys, I tried 1 more time, and I guess miracle does happen. Suddenly, it is very easy to reset the piston.
THANKS THANKS THANKS

And I think I got another problem. Now my brakes performs very weird. If I press the brakes very very very little, the brakes seem to kick in. If I press more then suddenly the brake is gone until the brake pedal is 3/4 way down and the brakes start kickin in again.

HELP HELP HELP AGAIN!!
TIA

did you loosen the bleeder valve?

Just drive the car and apply the brakes gently . I think the rears only do about 30% of the braking so it may take a couple of days to get full brake performance. Otherwise it's possible that if you loosened the bleed screw you may have air in there and may have to powerbleed the system.(you should probably do this anyway if the fluid is old and discolored.

Could this be the problem?

I never cracked my bleeders when I changed my brakes and I still somehow got air in the lines. Any air at all will give you problems.