Question: I have an Acer Aspire 5532, and it used to have a scroll option on it, on the side of the touchpad. I used a regular mouse plugged into the USB drive for a while, with the touchpad disabled, but it broke and I'm back to using the regular touchpad. however, somehow the scroll option got disabled and after quite a bit of trying I still can't figure out how to re-enable it. does anyone know how?

Answer: 
I fixed the problem by clicking Windows » Start, typing "touchpad" into search and clicking on "update drivers".

Update Synaptics, then restart and it'll all be good.
just hit Fn (function key) and F9 at the same time. Same thing happened to me. Couldn't figure it out for a year. Felt like an idiot when I found out how to turn it on again.