T3 Won't Power On

[gmitch]

Went to use my 1100D and realized that the power switch was left in the on position. Camera didn't turn on, so I figured the battery was dead so I fully charged it and put it back in. Still did not turn on. Tried the troubleshooting trick of removing battery and SD card and letting the camera sit for a few days. Came back and popped in the fully charged battery and brand new SD card. Still did not turn on. I'm thinking about getting a new battery but I'm not sure if the battery is the issue or if the camera has lived its life. It was used by my parents for some sporting events when first purchased but then sat in storage for awhile. I started using it roughly five years ago when I started getting into photography. I used it a handful of times each year- vacation, Christmas, and some small photoshoots.

[ebiggs1]

There are only a very few things you can do to troubleshoot your camera. You did one of them already with the brand new SD. The next step is a brand new Canon brand battery and an assurance that your charger is working properly.

".. and letting the camera sit for a few days ..."

You already knew that wasn't the problem or going to help because it had already set for a long period of time, correct. A T3 isn't a good candidate for repair so a good working replacement is a better choice. Plus, the new SD and battery will not have been in vain.

[ebiggs1]

Addendum:

According to statistics  the typical DSLR camera lasts five years when all things are equal but some cases they can go 10 years or more. In your case you might want to check for corrosion if you left the battery installed. Rubber dry rots, lubricants dry up, mold, etc.