First of all,
You should run a good Big scan of your computer.
If you have to much file's in your computer,and your memory is almost full,
that causes lag.
here some trick:
1.Big scan your pc for decting virus and deleting them.
2.follow these step:
3a.click system tools
4a.click disk cleanup.
***Disk cleanup might that minutes TO hours***
it took me 19 minute
and then when your finish with disk cleanup go with this one.
3b.click system tools
4b.click disk defragmentation
*****Disk Defragmentation can take minute to hours****
It took me 2 hours.because i had 3/4 memory used.
and then good luck
thank me if it worked