hey all im new to this so dont laugh at me plz, i have this presario 2100 and the laptop doesn't want to read its own HHD, is it because i had to open it and replace the internal DC, because it broke and would not allow me to charge the laptop?? Plz help me i dont kno what to do and i tried the booting disc and all it says is operation system error and when i go to F2 it just says internal HHD - NONE!
plz help me with this problem.

Pull the HDD and reseat it.If that doesn't work open it back up and check everything and make sure all is seated and nothing else broke.