Is the calf turned out with other cows and their calves? If so its possible that the calf is 'stealing' milk from the other cows. If this is the only calf, and no other cows around, then pent the little bugger up. In about a day this guy should be good and hungry. Back his little butt into a corner, and straddle it with your legs in front of its shoulders like a head-catch. Pry the mouth open using the fingers of one hand and stick the bottle in the mouth with the other hand. Squeeze the mouth around the nipple a few times to get some of the milk dribbling out. Stroke the throat as well. Eventually the little guy will catch on. It WILL get hungry. Be sure it has access to water. This calf can be fed a bottle.
I have rodeo'd around with calves older than this and got them to take a bottle. Sometimes it just takes longer with some calves.
Katherine has some good points. If the calf is penned, he won't take the nipple because he can tell the difference between it and his mothers tit. You might think about coating the nipple with a little molasses or Karo syrup to help him transition, sometimes that will work - sometimes not. You may just have to let him get hungery(sp?) before he will accept the nipple. He is old enough that he would have been eating hay/grass, so make sure you have some good quality hay available for him to eat. If you grain your cattle, he would have also been nibbling on that prior to his mother's death so have a handful or so of grain available as well. Watch how much he eats, and adjust the amount of hay and grain accordingly.
When you've got that nipple in his mouth squirt a few shots into the back of his mouth. Scratch his bum or between hind legs just like momma gives him a few licks when he is nursing! Don't be rough or panicky. Take your time, be quiet no cursing or yelling.