Fuel pump problem or what !

Hi All,
My ultra reliable 04 (D3) Swing has started giving me trouble. Reading other posts it seems as thought it might be the fuel pump, but I am open to suggestions.
Here's what happens, the engine turns, but mainly refuses to fire, every now and then it will fire up but only runs on one cylinder, will not rev and then dies after about 5-10 seconds.
Ive put in a new battery and spark plugs today. When I operate the kill switch I get a weak sound from (the pump ?). It is different from the higher pitch sound I used to get. The F1 light comes on when the kill switch is on and goes off after a few seconds. It does not blink or stay on at any time. The V light is on because I need to replace the drive belt which I have ready. The bike has done 16,500 miles and is always garaged.
Any help would be gratefully received. Thanks Codge.

Might be worth taking off the right hand side lower panel (under footboard) & check the condition of the H.T coil connections ?
After refusal to start are the sparkplugs wet ? (Clogged air filter/faulty choke)
When it does start what are the rev's at idle ?

Hi
The plugs were slightly wet, Ive seen them worse on other vehicles.
The engine barely reached tickover speed before cutting out.
I will take off the panel you suggested and check it out tomorrow.
Thanks for your kind reply.