Snowy screen just pops up

Really have a Hitachi31cx4b or 31ux5b, but had to us one of the listed.Had a Zenith hooked exactly like this Hitachi 31" solid State Color TV. My son bought new LCD and have us this one which was working perfectly. Now when the Hitachi is working properly, the picture and sound is very good. We play DVDs, VCR, and have optional surround sound. Why would a TV screen that was playing fine just turn to snow and fuzzy noise. The aux show clear, V1, V2, V3 Then this next aux is where the sat channels are played. We have found the only way to correct it (that we know of) is to change the remote to TV designation, keep punching numbers on the remote, then occasionally hit the channel up button. Sometimes it will come back on right away and sometimes it takes several tries. Any suggestions? We have Satellite box, zenith surround sound, DVD player, and VCR. The surround sound is all that works with the DVD, not the TV speakers. The snowy screen and noise is very annoying, especially as a touchdown approaches!