Pads could be old and hard, rotor might be glazed, fluid could be bad, caliper piston could be stuck or leaking, master cylinder could be leaking. How far does the lever pull in before it stops? If it is hitting the bar then something is wrong. Check the fluid, it most likely needs replacing. If the lever stops before hitting the bar and can't be squeezed any further then I would get new pads for it, they are pretty easy to change and you can pick a cheap set up from bikebandit for like $35 if I remember correctly.
At least the bike runs good! That front brake is probably the cheapest and easiest to fix problem with these bikes, you are lucky