LCD screen flickers for some time after startup.

I'm using a laptop with LCD screen. Lately I have noticed that the display flickers whenever the system is booted after about atleast an hour. This occurs even if I close the lid while the computer is on to turn off the display and re-open it after more than an hour. Then suddenly everything is OK after about 5 mins. There's nothing else wrong, the colours are all in order. I don't have any graphic card and my display adapter is- Mobile Intel(R) 4 Series Express Chipset Family. I've got Windows Xp and Ubuntu as OS and display was OK for both of them about a month ago. (Though this used to occur last winter, I ignored it thinking it to be due to low temperature.) In fact flickering occurs even while booting. What's wrong?