I had a similar issue in my 97, I'd hit a bump and the radio, along with the power windows, would quit working for a short time and then they'd start working again. For me the problem ended up being a bad connection on the BCM/ECM.
But what could be wrong is a bad connection on the back of the radio, a bad R.A.P. (retianed accessory power) module or a bad BCM/ECM.
Here's a link showing the location of the R.A.P. module:
http://shbox.com/1/express_down1.jpg and the BCM/ECM is located behind the access/knee kick panel that under the glove box. (sorry don't have a pic for that)