Could yo confirm that you use the keyboard combination to activate external screen?. If this is correct then your graphic card may be faulty. If not, the inverter of your laptop screen may be faulty.
Talking about buying a new one for this price, no way. If this is a second hand notebook, probably you could find something a bit better, but no so far froms that model.
Well i guess you are asking if it's a good price 310€ for this laptop. Yes it's fair. But take a look for the exact model, Pavilion models have problems with motherboards and screens.
OT:Are you spanish?