After years of operation, the tracks that the windows go up and down on can collect dust/dirt, and/or the grease that was used initially can get crusty old.
If you're ambitious, remove the inner door panel to gain access to these pivot points. Clean off the tracts, and any other points that rotate when the windows go up/down. Relube them with a good lubricant; I like the stuff that comes in a spray can used to lubricate motorcycle chains; they too get lots of abuse from the outside elements. This can has a small red straw that helps pinpoint the lube spray to where you want it to go. While I like WD-40, it's not a good perminant lubricant for the power windows.
Then open/close the windows to see if this has helped. Also check the pivot points or tracts for wear. If theres any slop, this will put a strain on the up movement. Windows going down is almost always good, as you have the weight of the glass and gravity to work in your favor; it's the "up" that works all the components the hardest.
Another point of failure is that the window switches themselves get corroded from use. The tiny copper or carbon contacts get worn. If these switches are able to be opened up, a piece of fine sandpaper can be used to clean off these contacts. If the switches are a culprit to inoperational windows, they usually just fail though; no open/ no close.