The render window was working just fine yesterday. But today, I can't hold the mouse wheel to move around. There no way I can continue modding if this problem persists.

you can also use space+mouse to do the same.

and check your preferences what it says for grid, might be 0 if you can't move and snap is enabled

Thank you so much!!! The spacebar tip did the trick. And I checked my prefrences: Movement speed is 1.0, snap to grid is unchecked, and I have no idea what the 256 next to snap to grid means.