Cable Modem resets itself

I have a cable line coming into my room that is split(5-1000mhz splitter) which goes into my cable modem and into the cable box for the tv. The cable modem (dlink dcm 202) is hooked up to a dlink (di-624) router running version 2.70 firmware. I have 3 computers(all xp) and a ps3 hooked up to it. Ive been working with this problem for about 2 months now.
The problem is my cable modem resets itself. At first it was the router then i did some research and found i was using the latest firmware and it has problems, so i found a previous version (2.70) for my router and the router hasn't reset itself since. It seems the cable modem resets whenever my mom starts using the internet from her computer. She doesn't have to be downloading anything, could just be browsing ebay or email. I have tried another router to see if that was the problem and the cable modem was still resetting itself. This problem doesn't happen all the time, just quite frequently when she is on. I am a gamer so needless to say getting disconnected whenever she gets on is quite annoying.
I have charter communications as my internet provider.

Any help would be greatly appreciated, im about to go buy another cable modem because perhaps this one has gone bad, but i wanted to see what other people think before making that investment.

thanks,

Brandon