Okay.......question time:  1.  Do the keys hit the platen, or do they just stop short about two inches without even so much as spacing the carriage?  2.  Does the ribbon vibrator come up when the type bars meet the platen?  My somewhat educated guess would have it that it's the former (#1), in which case you have a margin stop problem.  Something has engaged the margin lock, preventing the type bars' hitting the platen and ribbon.  The left margin stop pivots.  This stop, ironically, operates the right hand margin.  These machines are NOTORIOUS for sticky margins.  Tranny fluid time.  Get you a tooth brush and small paint brush, and start dabbin' that stuff on both sides.  Now, on the right stop, if I'm right, that sucker's frozen in place (Underwood Old styles are NOTORIOUS for this too).  Try moving it by hand, but if you can't budge it, every so gently tap on it, moving it towards the left, using a small screwdriver or chisel and a small hammer.  Do not hit it to hard--just tap it a couple or three times until you can manually slide it.  Slide both margin stops, and exercise the left stop by pivoting it.  You should hear the bell each time you pivot it.  Wipe out the excess oil, which will also clean out a lot of the old dirt with it.  This should  solve your trouble.  Let me know how you come out.

The typewriter is supposed to automatically disengage that lock when the carriage is moved from that stop.  I have had to use the margin release from time to time with old style Underwoods when they would get sticky and need cleaning.  Clean and oil them real good, and you should be able to type with that machine just like you would with any other, without having to use the margin release each time you return the carriage.  Would you believe Underwood was building their typewriters like this until late 1953?  My mother had one.  I found it outside a dumpster in 1985 when I was going to high school.  I took it home, unstuck everything, and gave it to Maw.  It reminded her of her original 1947 Underwood Rhythm Touch, only the carriage was a one-piece aliminum frame instead of the two-piece cast-iron one older Underwoods used.  Anyway, I used this same typewriter to do my senior year research paper that was graded by both my English and Government teachers.  Got an A on it--thanks to Maw's help.  Anyway, years later, I swapped her typewriters and gave her a 1959 Underwood Touch-Master II.  I repainted the old one and sold it for $60.00 or something like that.  I lost Maw 13 years ago, and I still have that last typewriter she used.  That one will NEVER get sold.