Dell E4310: preboot too slow....

I have a Dell Latitude E4310 with configuration is: CPU Core i5 M560, 4GB Ram (1666) and SSD 256GB.

After turn on, it spends 15 secs or more to appear Dell logo on screen. On the other laptop, the preboot time is 5 secs.

I try to replace RAM, update the bios with latest version, but the problem is still there. Please show me the way to fix it.

Thanks a lot.

Tran