i know this is a very old thread , but i am putting solution for everyone here. hope moderator will not have any issue with this :-)
i have solved this problem 5-6 months before, my friend had a same problem,
see first of all download exact driver for your laptop from lenovo site,
step 1 ) uninstall all existing drivers [ go into device manager (windows Key+pause/Break Key->Hardware Tab-> Device Manager) and uninstall all installed driver]
step 2 ) Clean Your Registry with CCleaner
step 3 ) Restart Your Laptop
step 4 ) Clean Your Registry again with Ccleaner
stetp 5) Now Install the Driver you Have Downloaded from Lenovo's official site and then restart your pc when asked, do as many time as it asks.
Step 6 ) Your Problem Solved :-)
If you find any difficulty with sound driver then pm me ok

Hope this will help you.