07 intermittent no start lights go out no power

so this I am hoping is a relay but unsure, turn key and nothing power leaves and sometimes comes back and will flicker or dim. turn again when power comes back and may start and then runs fine, also open drivers door and power might come back?.last night driver door wasn't helping I had nothing power wise then opened passenger door power came back started. sometimes when shutting car off and open door radio stays on sometimes it shuts off and then there is a buzzing in speakers...a gremlin maybe? any help would be great!!

First thing I would do, make sure key is out of ignition, nothing on....

Then disconnect the neg bat cable first, then the positive.....make sure there is no corrosion on the cables, or the bolts....clean if necessary.....

Check pos battery cable connection at starter, that it is clean/tight......check neg battery cable connection on block, that it is clean/tight..... apply dielectric grease to the contact areas of cables and attach positive cable first to battery, and then the neg cable....make sure tight, but don't over tighten....

If problem still exists, could be a bad connection somewhere, or an ignition switch problem.....