First, make sure your gear is ok. Take that carbon/titanium/aluminum/steel/plastic/paper steed to the shop and make sure that it's ok and can still be ridden. A full year without use can randomly cause issues you've never heard of.
Ok, dont' take this the wrong way, I'm just trying to get more information to make a proper suggestion because some things don't add up.
You did and was able to hit 100km in one day, but your weekly workouts were no more than 10km over a 2-3 hour time span, with breaks in between. This means you were riding no faster than 10kmh?
I understand you don't have to be a speed demon or have very high intensity during exercise, but 10kmh is like...rolling speed after two pedal strokes.
If you dont' feel like sharing anymore info, no worries, I won't dig.
As @Liuboy said above, just do a good warm up to get the blood flowing. High cadence with sustainable heart rate. You can do some stretches aftewards, but if you got a good warm up in, it's not necessary. Personally, I had a knee injury not too long ago due to not warming up properly, so I always get a bit of stretching in after my 20min warm up.
Like I said in another thread, just keep adding mileage. If you do x kms on day one, do x+1 the next day and keep on adding. You'll be back in shape in no time!
Hope that was helpful!