Where you live in the country is going to have a bearing on this type of problem to some extent. Post your location is a good ideal better yet even is incorporating it in heading. Anyways any unsoldered connection can oxidize if the climate is not dry. Or even in dry climates perhaps dissimilar metal corrosion can cause problems. Make sure the fuse holder is clean even if the fuse is good. If click type on and off switch on radio it can oxidize sitting as well. If radio not stock unit check installers electrical hookup connections. Get a test light or voltmeter to make sure voltage is reaching radio. If storage conditions are not pretty good I always expect some electrical problems after car sitting unused for months if stored in less than optimum conditions.