Thermostat went splat!

Our thermostat has kicked the bucket.  The day before we left on vacation I noticed it was cold in the house and the AC was running.  I went to check the temperature it was 4 degrees colder in the house than what I had it set on so I thought maybe Ray set it down for some reason.  When I tried to set it back up the buttons wouldn't push and finally it showed me it was set for 45 degrees.  I checked the heat and it was still set at 68 but when I tried to see if I could change it and hit the up arrow all of the sudden the number plummetted to 45 degrees.  So now I have to turn it on manually when the house gets too hot.  This weekend we are going to go and get a new one and hopefully we can figure out how to install it although Ray's friend told him it was really easy.