"i've downloaded the latest driver (which i am not sure whether it is suitable driver"
That suggests you may not have downloaded it from Dell's website, in which case it may well be the wrong one.
Did you check for driver errors in Device Manager? (chances are there'll be at least one).
Drivers for Dell laptops should only be sourced from the appropriate regional Dell website:
(If necessary, change region or country via link at top-left of page)