Why? Did you made the cable yourself? Just search online for FTDI usb cable pinout... I believe it involves a chip, due to usb, unless you want to make a direct rj45 to serial which i happen to have one lol. Cisco switches and such use them in both the true serial and usb variants that go into an rj45 jack and serial/usb on the other side. Oh, if you are using a true serial port, make sure its enabled in the bios. Some bios are set to "auto" and won't turn it on if nothing is plugged at boot.

I haven't touched putty in over a decade, but if it can do true serial then its a matter of picking the right port and speed parameters (115kbps 8,n,1).
If unsure test the program with something else if you have anything that still connects via serial (such as the aforementioned router, or an old fashioned pc).