I just want to reiterate some of the things Lydia said.
I started mostly with diet -- I cut back on portions and brought a healthy lunch and snacks to work. For exercise, I just tried to "move more" at first -- rather than yelling something up the stairs to hubby -- I WENT up the stairs.
If you're overwhelmed it may help you to take baby steps. you can do 7 minutes now? Next week make it 8. Then 9. I think sometimes we push ourselves to do everything, can't, feel like failures, and quit.
As for 80 pounds being a lot, yes, it is. But don't think of it in such big terms. Do you think you can lose 5 pounds? Focus on that first. Then the next 5.
Finally, I think it helps to have goals other than the scale. So many things affect our weight: water retention, TOM... and weight loss just isn't linear. So I find it helps to have other goals along the way. Yours might be the first time you do 10 min on the bike at a time, or counting the number of days in a row you exercise... things that you CAN control!
My 5 C's of healthy living: Commitment to conscious control, with the understanding that choices have consequences