Question about my bike chain

[frogprincessashlie]

I have never worked on a bicycle before, but i got out my old bike to sand down and repaint. i've been taking it apart and putting it back together so i can use it while i'm working on it. but this last time i can't get the pedals to push forward. they keep locking up. i'm pretty sure i have the chain on all the right sprockets, but please let know if you have any advice or tips on what i'm doing wrong.

[cyclerUK]

Unhitch the chain from the chainset and see if the pedals turn easily.<br />
Spin the back wheel to see if that's free.<br />
Check the chain to see if that has seized.<br />
With the chain back on, support the bike off the ground and turn the pedals.<br />
Does the chain grab the chainring when trying to turn?