Well, your not giving many specific details, why don't you just boot up with the old kernel and reconfigure the new one, compile and reinstall.
If you didn't keep your old kernel, then shame on you
, you can use one of the kernels of the slackware CD, put in disc 1 and follow the onscreen instructions to boot your installed system with one of the CD kernels, then do as above.
As your not giving many details I assumed you installed it correctly, but missed something vitial out in the configuration, as thats my most common problem when installing new kernels