Could be the keyswitch. If it's cherry blacks, it'll feel pretty stiff.
If you need to make a keypuller, you can do pretty well by bending some paperclips, or using a butter knife and being very careful. If you don't need it for long, you can get a nice wire keypuller from somewhere, and sell it to me when you're done. I've been needing one for a while.
Also, while you're at it, check the underside of the keycaps to see if they are doubleshot.