Windows7 freezes pc


Yesterday I got an update request from Microsoft to update my Windows 7. I accepted because I thought I had to. After it installed the update I carried on using pc successfully. Later I left it in standby and returned afte
r 2 hours. PC booted up, accepted password, displayed desktop. I clicked on Yahoo, and when I tried to open an email the pc froze. Mouse does nothing, keyboard is dead . I have tried shutting down and rebooting in safe mode. I cant get past the login screen. Can anyone help please. Thanks, Ronnie