Mine 8X blinks when I mistakenly put it on the microUSB Charger cable of my "Momo7 DualCore" tablet - it is slightly different charger I think because when I put a normal microUSB charger on this tablet it charges too slow. With other chargers my 8X charges normally, steady red until the end of charge then green.
I think you have either faulty charger or failed battery! Try other charger first. Else return it to HTC Repair Center or you carrier service centre.
As for charging for a 3-4-5 hours it means fully discharged battery. This may help really but I am sceptic. Try it anyway.