HELP in connection RS232 cable

Hello, i am new in the sat world, i like this forum so much because it's clear and organised.
i have one newbie question,what are the steps in upgrading or flashing a sat receiver through serial cable?
i have a he@d receiver HD500FTA and null modem cable, i connected everything as stated and satrted the loader tool but i arrive at sending the files without any response from receiver.
even i can't manage the frequencies through another utility. i checked the com ports which are ok, but i still have no clue what i am missing
thanks

thanks for your help, i had already the loader tool and the firmware, but it says "can't open serial port" is there a tool to see the com ports under XP and configure them?

my serial port was disabled from bios, i fixed the problem now. thanks for everyone