DREAMBOX 5OO C

Hi chaps, i am wondering if any kind soul could give me some assistance.

I have a DM500 C which was working perfectly well until i started to mess around with it and done a factory reset, yup lost all the software on it to decode channels.

I understand i have to use something called dreamup to flash a new image etc to make it work properly, the trouble i am having is that i have a laptop with no serial port, so i have bought a null modem cable and then a usb converter thingy to connect the box to my laptop in order to flash it. When i run dreamup it does not detect the box... where am i going wrong??

Many thanks in advance.