system not working due to South Bridge failure

hi,

I have a Dell Studio 1555 laptop approx 4 yrs old.

One day i put my laptop on sleeping mode and after that it did not open at all.

When i press the power button The power switch light comes up and DVD drive starts along with Fan (cooling system), but LCD does not start. 

When i checked with the hardware engineer  , he said that  LCD is okay but South Bridge has failed .(not working).

Can anyone please help me with why this is occurring again and again . This is the third time south bridge has failed.