Quick Question about clutch

[s13rookie]

I start my car this morning, already running late for work and i almost put the clutch pedal through the floor. There is no pressure on the pedal. I check the resevoir and it is full to the top. I assume its either the slave or master cylinder. I have had those go bad in the past, but there has always been a loss of fluid that went with them. at napa the master is about $90, and the slave about $40.

Which one would be the most likely to have gone out? and can they go bad with out losing fluid?or should i replace them both at the same time to be sure.

When i get out of work tonight, im going to try to bleed the lines to see if they may have gotten air in them somehow, but i doubt that is the cause.

Thanks,
Matt