My outside electrical outlet just stop working. I installed X-mas lights the day after Thanksgiving. Everything was working fine for the next couple days. It rained that Sunday. The next day when I went to plug in the lites to the outlet outside and the lites didn't come on. I got another power cord and plugged the lites to it and plug it up in the house and everything came on (all lites). What could be the problem with the outlet outside?

You probably tripped a GFI feeding the outside receptacles.

This can be in many different places. First check other outside receptacles to see if one is a GFI device. They check to see if it is a tripped GFI breaker.