Optoma HD70 Lamp will not come on after replacement. The power light comes on and fan runs...but the Lamp will not light up.

SOURCE: Optoma EP755 new lamp when power standby button

you need to reset the lamp timer, usually done by holding some buttons while turning on

SOURCE: replaced lamp on optoma hd70 unit will not power on

I had the same issue.
Take the bulb cover off and hold it just above the unit. notice how that part that sticks down has a little curve to it. The curve is designed to gently push that little metal wire as the cover is lowered.
If you take a small toothpick and exercise the little wire in... NOT DOWN... you will hear a small click. That is the switch making contact. When it makes contact and clicks... and you plug it in the green light will be on again... and the unit will work fine.
You do not have to take the tabs off.
Just exercise the switch... put the cover on slowly... be very quiet and you can hear the click sound.
Plug it in and you are good.
And if the color starts to flicker on and off... it needs a VERY good cleaning... not a new bulb. Read my other posting to the guy with the fan picture.
Doug

SOURCE: Optoma HD70

Call 1-888-942-2929 option 2 the cost is $59.00