This may be a screen resolution problem rather than a font size problem. You should download
the hardware (motherboard and video) drivers
from Dell. Windows might not have the exact driver for your video chip or other hardware on your motherboard. Laptops always need a driver update after a Windows re-install.
You might first try to change the screen resolution from the (640x480 Safe mode)
Right click on any empty area of the desk top screen.
Left click "Personalize"
Left click "Display Settings"
If the system allows you - Click and drag the resolution slider to the far right to "(High)"
If the slider is grayed-out then you know that a new video driver is needed.