Most Dell systems have beep codes that are in groups of three, so I don't know for certain what yours is saying. But after a fall it's a good bet something has come loose inside. I would suspect memory first. Take the cover off and make sure the RAM modules are seated firmly and latched into their sockets.
This page at Dell shows you where the RAM sockets are and details how to install memory. Also be sure the processor is firmly seated in its socket. Unless the computer really got knocked about, the processor is likely to be okay; it's pretty well secured and RAM is more often what comes loose.
Without the RAM properly operating, nothing else in the computer will happen properly when you start it. Once you've reseated the memory in yours it will probably start up without further troubles.
(And as a fellow cat owner I feel your pain. Unfortunately it was an external drive that my cat knocked off the desk, and it didn't survive the fall. Lots of music and videos gone now...sigh.)
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