On Sat, 04 Mar 2017 20:48:57 +0530, Archer
wrote:

Tried to install Windows 7 Ultimate using a spare hard disk (put in
place of the original one). I had to set the BIOS to Legacy (instead
of UEFI).

The install went very well but none of the USB work. I tried USB
drivers but no improvement. I have also read so many sites in Google
on G50 lappie but could not get the solution.

Lenovo offers drivers and application for Windows 7 for this product,
so it is very strange.

Did you updated the BIOS?

What exact version is your G50-80 ?

G50-80 Laptop (Lenovo)
G50-80 Laptop (Lenovo) - Type 20371
G50-80 Laptop (Lenovo) - Type 20523
G50-80 Laptop (Lenovo) - Type 20642
G50-80 Laptop (Lenovo) - Type 80E5
G50-80 Laptop (Lenovo) - Type 80KR
G50-80 Laptop (Lenovo) - Type 80L0
G50-80 Laptop (Lenovo) - Type 80L4
G50-80 Laptop (Lenovo) - Type 80R0
G50-80 Touch Laptop (Lenovo)
G50-80 Touch Laptop (Lenovo) - Type 20516
G50-80 Touch Laptop (Lenovo) - Type 20527
G50-80 Touch Laptop (Lenovo) - Type 80KR
G50-80 Touch Laptop (Lenovo) - Type 80L4

Go there
https://support.lenovo.com/us/en

and search for G50-80 and choose the correct one.