Replacing a water pump is easy .. but that's not likely your problem.
The water coming out the hose inlet accounts for the "no pressure" .. there is valve in there operated by a springy thing which is stuck open - you might get lucky and reset with small screwdriver or even attaching hose and turning on water for second or two .. not expensive or difficult to replace.
Once the outside water issue is resolved .. put some water in your tank, turn off faucets, turn on pump -- pump should turn on until system is pressurized and then turn off. If pump continues to run or periodically turns on then you have a "leak" and need to examine hoses/connections to see where it's leaking.
