I work in a building that used to be under high security, so my office has no windows. To combat this, I fill my desktop with nature photos and try to decorate my desk with things that make me smile.
On a daily basis! LOL! I'm a stateworker in CA and have been fortunate enough for most of my tenure here to occupy a cubicle with windows. The view ain't great, but it's better than nothing. Even with that, I have personalized my cubicle with lots of pictures of my kids (my daughter is a performing arts nut (age 16) and I have pics of her in all of her roles, plus some other pictures and misc items I have received as gifts, including several Star Trek holiday tree ornaments (complete with sound!). You could also install a personalized desktop background (wallpaper) on your PC if it's permitted. Hope that helps.