Ballast/lighting question

[marie]

I have 3 single ended 250w bulbs (lumenmax elite pendents) with 3 250w HQI ballasts which have run flawlessly for 4.5 yrs.
A few days ago a bulb didn't fire, the bulb was about 9 months old so I assumed it was done for and replaced it with another 9 month old bulb that I had. Today it went too so I replaced it with a 6 month old bulb and it didn't work, I then tried a 1 month old radium bulb and that didn't work either.....So I figured I needed a new ballast....tonight another bulb on a different ballast went. Is this coincidence? Am I going to need to replace all 3 ballasts or could there be something else going on, the ballasts are warm like they are when they are working???? I don't want to replace all the ballasts if I don't have to