RS-232 interface chip problem - why is the voltage level so wrong?
The outputs and inputs of your circuit are labelled as a DTE connection: a Data Terminal. Your PC is also wired that way. 

But RS232 works on the basis of a DTE-style device connecting to a DCE-wired device: Data Communications Equipment, i.e a modem.

To fix this, swap pins 2&amp;3 in the connection so that Tx on one side connects to Rx on the other, and vice-versa for the other wire. Leave ground as it is. (You can either swap RTS/CTS or leave disconnected)
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(From https://www.decisivetactics.com/support/view?article=crossover-or-null-modem-vs-straight-through-serial-cable which also has additional discussion)