The arm can go up and down about two times and then it just stops, even without the third stage attached.
Video: http://youtu.be/CHhtGwzxY44
If you give the motors some time (5-10 minutes or so), will the lift work again? I’m wondering if your motors might be overheating and tripping out their PTCs, which are little devices in the motors that shut down power to the motors when they get too hot from being overloaded.
Have you checked to make sure your slides are fairly easy to move without motors? Sometimes if slides are non-parallel with the direction of motion, the amount of friction generated can be excessive.
That looks sort of familiar.
Probably friction.
Without the chains that stage should fall on its own if you lift it up and let go, does it do that? Getting the exact spacing for the linear slides takes time and the addition/removal of spacers (ie. washers) as necessary. The green slide trucks needs accurate setup so they are parallel.
Are both motors working together? ie. is there a chance they are working against each other or is one disconnected?
Thanks for the suggestions, I’ll adjust the slide trucks on tuesday ( when I have access to my robot ) and get back to you guys on the status of my robot, Thanks 
My team had a similar issue with a different style of lift. The issue was just that the motors drew too much from the batteries at once, so the battery needs a moment to recover. We ended up adding elastics, reducing friction with washers, adding 2 more motors to the lift, and most importantly, changing our gear ratio from 1:3 to 1:7.
Hope these help!
In addition, be sure to keep the outer derlin slides a bit loose; if they are too tight, the slide can’t even fall down with gravity.
And like jpearman said, the amount of space between the slide and derlin slide is very important. With CAD, we found using two teflon washers between the c-channel and the slide on both sides to be perfect. In the picture, the only reason we added the 0.5" spacer to the two teflon washers was for a wider lift but it works well without it. Hope this helps 
