Guinea Pig Not Eating?

[primrosette]

Hi!
Recently I've noticed that one of my guinea pigs, Oliver, isn't eating his pellets or hay. I rescued him so I don't know any previous sicknesses, but he's about 1 year old. I rescued him with another guinea pig, but they did not get along, despite the fact that they came together.

On Wednesday, I noticed him chewing on some cardboard that was attached to the hay rack in his cage (to keep hay from falling out the sides. I use a bent grid as a hay rack).
On Thursday, I noticed that a big chuck of the cardboard wad gone (he ate it). Later that day I removed it, but he wasn't eating it, or his pellets or hay.
My other guinea pig, Charlie, always eats all his hay and pellets.
Today, Friday, he still isn't eating. I had him in my lap last night and he ate a Nibble Ring and nibbled a lot off of a vitamin C treat. He also ate a small bit of an apple.
Today I cleaned his cage as well, it was disgusting. I didn't know how gross it was, he sleeps on his pee.

I'm extremely worried. He's still drinking though. I'm going away this weekend and he will be under my parent's care.
Does anybody think they know why he's not eating? PLEASE ANSWER!

*Note: The hay that I currently have is a hay that neither one particularly like, however I've seen them both eat it in the past. It's the only hay that my pet store carries, and I use it between orders of KMS Hayloft.

[furzechan]

A guinea pig can die if it does not eat for 1 day. Please bring it to the doctor for proper treatment. This is an urgent issue, no kidding.

[bpatters]

He may have an intestinal blockage from the cardboard, or something else. Or he may be ill, or have teeth problems.

Failure to eat is a medical emergency for a pig -- please get him to a vet that knows something about guinea pigs ASAP.