If you have two computers that you leave on all the time, you can create a simple daily job (I think Windows calls them "scheduled tasks" or something) on computer A to backup it's important files to computer B.  And another separate job on computer B to backup it's files to computer A.  So it's totally unattended and automatic.  Years ago I used to do exactly this using a free program called SyncBack.  Get it at 
http://www.2brightsparks.com/downloads.html - scroll down towards the bottom to get past the paid versions to find the free one.  That's probably all you need.  Now I have a more sophisticated backup procedure using a Linux server to control things, but that old "A->B, B->A SyncBack" Windows routine worked very well for many years.  I didn't sync the entire computers, just the important personal files that couldn't be regenerated by reinstalling the operating system.  Documents, photos, music, etc.