iMac mid-2010 starting crashing and apps failing to launch after latest 10.9.5 update

A few days ago my mid-2010 iMac started crashing for the first time since I bought it in Nov 2010. It crashed 4 times in 3 days. Just got a white screen with a message in a square in the middle that said the computer needs to restart.

Yesterday Mac apps - Calendar, Preview, iBooks, FaceTime, etc. - started failing to launch. Checked and repaired permissions, Disk is OK I get the message “Preview quit unexpectedly” when I try to open it. It says “Bug in libxpc: Domain bootstapper failed to respond. it is likely crashing in a loop”. Same for other apps.

I am so amazed after this machine has run without crashing or failing for 4 1/2 years, I am suddenly having these issues.

Is this a software problem .... or is the hardware just giving out?