My acer aspire 4310 doesn't boot up

hi i have a acer aspire 4310 laptop.whenever i switch it on it shows a white screen.i have to again and again switch it off and on till it boots.this makes the windows software corrupt and so my laptop has been formatted 5-6 times.i have sp 2.moreover when it boots up the welcome screen is shown for a long time and then the wallpaper is shown for an even longer time without the taskbar and icons and yes the dvd player also doesnt work .i have replaced it two times.someone said that the bias may be lose....(what does that mean?).plz help me solving this problem.............