2003 Speed Triple Not Starting

Hello from British Columbia, Canada.
I'm just about to start my second season with this 2003 Speed Triple. Love the bike! At the end of last season it was starting take a little time to start, ie: I had to hold down the starter much longer than previous. Being a relative newbie to mechanics I thought I'd start with a tune up...changed the plugs, cleaned the air filter and changed the oil...the easy stuff. It was also recommended to me to add some fuel injector cleaner to a full tank of premium gas and take it for a ride. So I did this, but, full disclosure, the tank had some 4-5 month old gas in there from last season to which I added some fresh gas.
Anyway, the initial ride was fine. In fact, it felt like I was getting a bit better performance. My problem arose the next day when it wouldn't start at all. The plugs seem fine, there's fuel getting to the fuel rail, fuses are good, starter is turning well, battery is good, and I believe I'm hearing the fuel pump working when I turn it on.
Does anyone have any suggestions of any DIY things I can try?
Huge thanks in advance.