I Want To Go Back To Yosemite

[thewall]

3 months ago i brought can iMac (new) with Yosemite installed when i switched it on i installed El Capitan but now some of my peripherals don't work properly,and sometimes i can not login the password box fills itself i have to physically shut it down.

As i didn't uninstall Yosemite is it in a partition and can i retrieve it or is it more complicated than that.

I had Time Machine but reformatted the drive to start new.

Also if i have to backup will my photo's go back in the same order or as 1 folder

 

[komatsu]

BEFORE you start any attempts of OS install, perform a full Time Machine backup.

You can install Yosemite with internet recovery

Press Command and R and when your Mac starts, this will initiate a recovery.

 

[thewall]

Thanks for that i have another question now my time machine looks like this,it hasn't saved any photo's or music etc does everything stay where it is when i reinstall Yosemite or can i set TM to save the photo's and music eat