Hi,
does your board have two serial (RS232) ports? Is it a Xilinx board? If so, the ports are one for internal uart (fpga) and the other for external uart which is on the board.
If you are implementing the uart on fpga, you need to use the internal port. Assign the uart rx/tx signals to the internal port pins and then synthesize and implement ur design. Then download it to the fpga.
After that.. don't power down the board... with the power on.. connect the cable to the internal uart port on the board and to the PCs serial port. Fire up Hyperterminal.. and select the baud rate and other settings as per ur design.. make sure that the uart settings in ur design match with that of the hyperterminal port. once you connect in hyperterminal.. you can send characters to the uart in the fpga by typing into the terminal..
Possible ways to check are.. the other end of the uart in fpga should be connected to LEDs or LCD display where the character will be displayed.. you could also connect to the external uart port and connect it to another pc running hyperterminal and check if the character ur sending from one appears at the other..