My HP Compaq Presario CQ60 won't turn on at all ! PLEASE HELP

Hello ,
I've got a HP compaq Presario CQ60 which doesn't Turn on anymore . The Battery and the AC Adapter are new and working . The LED next to the AC plug lights up if I insert the AC Adapter . The Power , Lighting and Hard Drive LED at the bottom of the PC are off constanly . I tried the 1 min thing with discharging the whole power . Still ain't workin . I know its an old pc but I got important files on it . I hope maybe someone has an idea . Another question , is it posible that everything is lost if I got a problem with the motherboard ? Cause I cleaned and checked the RAM too . Btw it happened from one day to the other . I'm sorry for this long text . Thank you in advance !

I forgot to ask if it is posible to check the Laptop with an Multimeter wether not a power cable or so inside may "broke" by overheating or so .