Compaq CQ40 cannot load desktop

Hi there, I have a laptop that my brother just bought second-hand and when he first turn the pc on... everything was fine.. the day after that everything began to be.. glitchy... first there was no compaq logo shown on startup with the F2,F8,F10 information.. but now it's just blank... n then it directly shows an underscore at the top left... and after that the windows 7 logo appear.. but half way through the win7 logo, the screen began to be kind-a glitchy , it shows a black screen in an instant.. then it shows black with the windows greeting that should bring me to the desktop but nothing... I cant try to add new task "explorer.exe" because there was no mouse pointer.... everything black n then I tried Ctrl-Alt-Del and then I randomly press enter I can see the desktop but again... the desktop screen only shows like half a second. n then black with no mouse pointer.. if you say that it is the screen, I think not. because the glitch happen on startup (the compaq logo is not shown) and after the windows 7 logo (the windows 7 logo plays smoothly no lagg or some sort) so there is nothing to blame on the screen..
Im still finding a way to solve this. so any information will be appreciated... TQ :)

Extra info
Compaq Presario CQ40
3 gb ram with 2 ram (1, 2gb)(2, 1gb)
running windows 7 ultimate
already tried the unplug everything (battery,adapter n then press the power for 10 sec) didnt work...
the bios is also glitchy, everything is blinking again and again at about 3 blinks per second...