Get Picasa from google, its an excellent tool for home use..
open the picture with picasa..
a *.jpg file opening gives a not vallid file error
solution to this is that the link in windows informs windows to open *.jpg with a program that is not correct win32 openable .
2 possible common causes.
the link is wrong
the file is wrong
for instance if you have extentions hidden , something could be displayed as namehere.jpg
what you wouldnt see is namehere.jpg.scr
and that would be a virus , but mostly people are warned enough about those nasty things so they have virus protection , and if that would have been the case your virus scanner would of had a busy day
so picking the first possible cause , the wrong link
easy enough you can right click on the jpg file and you can then select " open with " rollout menu to the side then the option open with if im correct wich causes a dialogbox to pop up informing you of a list of all the software programs currenly active installed in windows.
jpg file i would prefer to open with something that always works and normally present in windows either windows imaging ( wich is in the list ) or MS paint .