Hmm, well it should work.
See these:
http://www.virginmedia.com/help/ethernet/index.php
http://help2.virginmedia.com/help/ge...ced_cablemodem
Basically the same info as before, but also mentions releasing the PC's IP address first [can help some people sometimes, although I never found it necessary myself]. Also try leaving the modem off for a bit longer...maybe 5 minutes.
Do you have a different ethernet cable you could try? [perhaps the one you tried is duff]
Your PC has an ethernet port doesn't it? Try swapping from using USB for the PC to ethernet for the PC....[help rule in/out the PS3's ethernet port being the problem]
If trying different leads doesn't work, & trying the PC's ethernet doesn't work, then perhaps the ethernet port on the modem is faulty...