Hi,
Step 1:
I would suggest you to refer the below steps and check if it helps.
a. Click on ‘Start’.
b. Type ‘paint’ in search bar and hit ENTER.
c. Make sure you have two paint Windows open, stretch out the tile in both the Windows.
d. Go to ‘File’.
e. Click on ‘Open’, and then choose what picture you want to merge.
f. Next go to resize and type in the size you want your photo to be, go to cut, and cut your whole entire photo, and then copy.
g. You now want to paste the photo.
h. Now go to the other paint window, choose what other photo you want to merge, and then make it the same size as the other photo.
i. Cut that whole entire photo and then hit “copy”, and hit “paste”.
j. Now both of your photos are in the same window side by side.
Step 2:
If the above step does not work, then I would suggest you to use the Windows Live photo gallery to test and check if it helps.
http://explore.live.com/windows-live-photo-gallery-organize-edit-share-using