Well without knowing what the reg file did, this is just a rough guess. Below is the bog-standard mouse settings for the registry:-
Copy and Paste the info between the lines and save it somewhere as NormalMouse.reg then just double-click it.
------------------Begin Copy and Paste------------
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Control Panel\Mouse]
"ActiveWindowTracking"=dword:00000000
"DoubleClickHeight"="4"
"DoubleClickSpeed"="500"
"DoubleClickWidth"="4"
"MouseSensitivity"="10"
"MouseSpeed"="1"
"MouseThreshold1"="6"
"SmoothMouseXCurve"=hex:00,00,00,00,00,00,00,00,15,6e,00,00,00,00,00,00,00,40, 01,00,00,00,00,00,29,dc,03,00,00,00,00,00,00,00,28,00,00,00,00,00
"SmoothMouseYCurve"=hex:00,00,00,00,00,00,00,00,b8,5e,01,00,00,00,00,00,cd,4c, 05,00,00,00,00,00,cd,4c,18,00,00,00,00,00,00,00,38,02,00,00,00,00
"MouseThreshold2"="10"
"SnapToDefaultButton"="0"
"SwapMouseButtons"="0"
"MouseTrails"="0"
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