Elitebook 8440 Turns on for a second and turns off

[Xaydek]

Hi so someone brought me an Elitebook 8440 to repair. It was overheating so I cleaned out the fans and applied new thermal paste. However now the laptop turns on for like a second. fan spins for a second too.. and then it turns off.. nothing on the screen. i tried some methods I found online such as removing the ram, testing the hard drive. disconnecting all power sources and holding the power button for a minute then put the power source back.. nothing happened. I thought maybe I applied a little too much thermal paste and it was short circuiting.. it wasn't that.. the paste was applied properly..  please help

[Xaydek]

anyone?