I am restoring the same Pavoni as yours but with two groups (P3V2). It's a superb machine that is very well built, so if I were you I'd try getting it to work again.
I faced very similar issues when I first started up my Pavoni that hadn't been used in 10 years.
1. The Procon pump is probably stuck like mine was. Turn the machine off, separate the pump from the motor, and try turning the pump's shaft with a wrench. Put it back together and see if it works when pressing a brew button.
If you have the machine hooked up to a water line, this is sufficient pressure to fill the boiler. Both steam and hot water are connected to the boiler. To get water out of the groups you need the pump to work.
2. There is probably some scale in the copper pipes. Descale the machine to solve the problem. Do a search to find out how.
I hope this helps!