Latitude C840 70w Power Supply

I just got a universal power supply for my laptop since dell sent wrong one. I was wondering why it wont charge with it? when i first loaded windows it gave me a massage saying it couldnt work right or something. and if i hit f1 it would run into windows and f2 would reboot( i got this screen right before loading windows) then when i loaded windows i got another message asking if i wanted too do the power management. and i clicked yes(it was a gray screen) When i clicked it it was fine, windows was loaded and i was recharging. I restarted cause when i flip my lid the screen wont come back up. And when i came back, it wasnt recharging. Anyone know why?