I read the other two posts and you may have to replace it as Ed said. You can get a good quality door for $500 installed and you can also spend a lot more than that. Look around. Get a wood door clad in vinyl or steel, double pane glass, low e, argon, easy slide, etc. Also think about french doors.
I just replaced a 20 year old door that measured 1.5" wider than any standard 6' doors today. Not sure if that old one was an oddball door or if the standard changed. When they put in the first door, they sided and remodeled inside. Let me just say that a standard easy change out turned into a complicated shimming process and then redoing and scribing in the interior trim and making trim pieces that looked good with the metal siding.
If your track has a small dent in a rail sticking up in the track which then causes the dented rail to spread so the door rollers won't roll right, I would try getting a hammer, chisel, and some other metal working tools to try to fix/straighten it first. It may be that you can cut out the bent part and make it work. It may or may not work but may be worth a try depending upon how big the damaged area is. Good luck. Post back if you fix it that way.