This is one of those frustrating problems that many people with multiple monitors have had and the resolution is actually quite simple

• Right click on the desktop, click screen resolution.
• In the dialog where you see two monitors drag them so they line up.
• You should notice the jump increase and decrease with the alignment.
• Ensure that the screens are lined up on the bottoms.

Done!! Now your monitors should be lined up perfectly and your mouse should move across them.