Strange issues; maybe electrical, please help?

Last year, I was just driving down the road and hit a bump. As soon as I did,
the radio went off, I couldn't operate the front windows (the sun roof open as
do the back ones), 4wd stopped working, gas gauge stopped working and
the display showing what gear I'm in stopped as well. Through out the past
year, it will often come back on for about 5 minutes and then stops again. I
can get the radio to come on on occasion if I turn the ignition very slowly.
Any idea what this may be? I have a 2004 Avalanche z71