About 2 weeks ago I had to change the alternator serpentine belt and battery in my car. We had a severe rain storm and the sunroof was open about an inch the inside got wet but the but started and I ran my errands came home the next day I go to start the HHR AND NOTHING NO LIGHTS NO NOTHING I wanted to open windows to help dry

 

Could be a number of things. 1st would be to check the battery charge.
12.6-12.8 volts would be charged. Any less than 12.0, have the battery charged up.

 

Welcome to the site, have you opened the rear hatch and accessed the battery to test it?
I suggest checking all ground wires, the fuse box under the hood and the passengers side of the console.
If you are going to connect a battery charger or jumpstart it , connect directly to the battery.
You can connect to the front red capped terminal on the fuse box under the hood ( see lower left of fusebox in picture) and the strut tower bolt for ground, then pop the hatch.
But not for a jump start or charger.

 

Like Old Blue said you can jump under the hood to give power to the rear hatch but if you try to start the car from there you will just blow the power steering fuse {don't bother to ask me how I know this}

 

You wouldn't blow the fuse if you followed directions in the Owner Manual and as oldblue wrote.

My bet is that the butyl patch has failed and there is a lot of water in the BCM.

 

x2 what Donbrew posted.

And contrary to some peoples opinion, jumpstarting from the documented points under the hood is totally acceptable. One just has to remember to connect the POS connection to the POS point under the RED COVER (the one with the big + sign)as shown by Oldblue, and the Negative to the labelled point on the strut tower.

Connecting the POS to the other uncovered red contact point will blow the power steering fuse, as many have found out.

 

Trying to use the small red one for ground will screw thing up as well. That is what usually happens when people who "know it all" think any large black box under the hood is a battery.

 

 

I’ve always connected directly to the battery posts when jump starting or charging the battery . To avoid over heating the wiring or cooking the computer.

 

My engine compartment seems to be missing the lines and letters, as well as the giant red X, please help? (joking)