From the added description, it sounds like the mainspring (if it is a flat-spring action) is in the wrong position. If the tip gets below the toe of the nose of the hammer during reassembly, you will have the symptoms you describe if you don't break something outright!
If you remove the fore end and take out the mainspring, then reinstall it with the lever closed all the way, that may eliminate your problem,
IF nothing got bent or broken in the process.
If it's a coil spring action, you probably will find the lever plunger and spring and/or the mainspring placement in the hammer/block sub-assembly are wrongly assembled. Other than destroying a coil spring (which again will be hard to replace) the rest of that shouldn't be too bad to fix.
If you think the action is pretty complete without any other damage or missing parts, I would go a little higher than previously posted... maybe start at $350 and go up to maybe $500 or so if, and again I say
if it seems like that is all that is wrong with it and the outside looks OK and free of the abuse from whoever put it together wrong and whoever let him.
Since I have the parts it would be likely to need (probably) I would think seriously about offering $500 if I could look at it and assure myself that was the extent of its problems. JMHO, and worth almost as much as you paid for it!
Froggie
PS If it's anywhere near Central VA and you decide you don't want it...