bios taking a long time to load

I bought my computer 3 months ago. Never had hardware/bios problems, everything was great. But since a while, when I power up my pc (plugged and on battery), I see the DELL "loading page" and everything looks fine, but it takes a certain time to load. Recently, I had a warning that I must use a 130W power supply for my notebook, but nothing was changed : I use the same power supply that Dell shipped me.

I'd like to know what could cause a slow down on the bios when nothing was changed on my puter