It is the router, and as you have only had it a few days see if you can return it for an exchange for a D-Link or some other router.
There has been on cable systems a consistent malforme packet attack on cable systems (not to date on DSL) that lead to your result with current Linksys firmware.
I can tell you at the moment there is not a resolution, but there is a lot of work being done to solve the issue.
But there is no killer firmware to date for your Version 3 router.
Discussion: (lengthy)
Note: This is becoming a serious issue, and one not ignored by Linksys. Several remedies have been suggested if you read the lengthy thread linked above:
. revert the firmware. If you revert to 10/2003 firmware for your router the problem disappears; see the discussion linked above.
. Swap the router from your sales dealer for another brand. It appears the attacks are squarly focused on Linksys firmware vulnerabilities for malformed packets.
Everyone who uses Linksys products would love a killer fix for this; it appears in waves on cable systems, and it is more than annoying.
Please read the linked material above and make your choice. Personally, I wish I could offer something more affirmatively to fix this issue, but I have yet to see it. When I do I will certainly post it here.
Best,
Bill Castner