Try this:
Right-click on any picture file.
Select 'Properties'
Take a look at the name of the program alongside 'Opens with'. It should be whatever program you expect your pictures to open in. (The default program on your PC is probably 'Windows Picture & Fax Viewer' but you might have chosen to use something else, such as Irfanview or Picasa). It's likely that the wrong program is assigned, so click 'Change' and select the correct program. Then click 'Apply' and 'OK'.
This reply is a generalized version of the reply, relating specifically to Dell PCs, which was posted by Sharron53 here:
http://www.dellcommunity.com/supportforums/boa rd/message?board.id=si_virus&message.id=44218
(Jim77345 reported that it worked for him, so I hope that it also works for you).
Chris