netstat crash....oh dear oh dear oh dear

Thanks for reading my miserable plea for help......
right then....i visited a friends house for the first time and saw her pc sitting quietly and her modem going like mad and asked if it was like that all the time...affirmative. i installed peer guardian to see the ips passing through which i blocked it was quiet. but wait something had altered the config file of peer guardian so i tried a netstat probe and the computer shut down and restarted. after the boot sequence began the modem started sending and receiving data while holding the boot sequence for about 2mins. when it started up peer guardian was useless entirely shot you couldnt use it to ban ip's.
she was using virgin broadband and the packaged virgin security. using diamond port explorer i found telnet and messenger very active so i stopped those services. after a restart the boot sequence was held up again more data transferred and all services were re-activated when it finally started up.
I thought that a better firewall would be a good place to start so i installed f-secures 2008 after i un-installed the virgin package which is pretty lame.
The problem is now that with f-secure installed when the pc reaches the point where before it started to transfer data the bloody thing is restarting a continuously endless loop of power on start sequence just when it gets to the screen that says windows is starting a split second later it powers off and starts again.
she bought the thing amd 2.4 75gb ntfs on ebay from someone who never provided a disk though i have one windows xp pro.
i thought about doing a re-format and install from scratch but have no idea what the motherboard inside is or what is attached to it and she has not a clue. i can get the machine to C: WINDOWS>_ but do not know what to do from here ANY help is much appreciated.
the drive has an 8MB partition and then windows xp not even sure that it is pro i think i saw system restore but cant be certain.
if system restore is there can i undo the f-secure install or capture the driver file settings they hold from C:windows>_aaaarrrrrrrrrgggghhhhhhh!!!!!!!!
What o great one is the way out of this nightmare?. and thanks again.
i just remembered that when i put my copy of xp pro in the machine it looked for previous installations and it didnt say that they were different. would it if home was installed and it was reading pro from the drive. as for the administrator password the person she got the machine from set that up and she didnt think to ask for it. :4-dontkno