Standby green light flashes constantly tv working but weak signal error appears

These blinks [flashes] are fault indication (Error Codes). From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit section inside it. This will make repair easy. These are called blinking codes. Make sure about the exact number of blinking of the standby/power LED, by switching On & OFF the set, for at least two times. Count it carefully. If you wish to get some details, check the site linked here. It has details about blinking codes, and fault locating procedure, to many popular brand TVs and other devices. http://electronicshelponline.blogspot.com/
Blinking codes details of many popular brand TVs are given. Surf the site with patience. If blinks continue without any pause, the main board is faulty.

Sounds like the main system control-chroma IC fault. These blinks [flashes] are fault indication (Error Codes). From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit stage inside it. This will make repair easy. These are called blinking codes. Make sure about the exact number of blinking of the standby/power led, by switching On & OFF the set, for at least two times. Count it carefully. If you wish to get some details, check the site linked here. It has details about blinking codes, and fault locating, to many popular brand TVs and other devices. Viewing it in "Mosaic" will make surf easy.
http://electronicshelponline.blogspot.com/
Blinking codes details to many popular brand TVs are given.

set is trying to move from standby to power supply on and not making it, No model indicated so best advice is take to some shop and get an estimate.

On Sony the standby or red is for shutdown---

If you unplug the set and plug it back and turn it on and it repeats this look to see if the light is either constantly blinking or blinking a specific number of blinks---specific number would be an error code.

Help Line: 800-111-4567

Is the projector receiving a source signal? if not it will power itself down after whatever time you have it set to do so when no signal is present.
Just an idea?

you need to test the lamp with a ohm meter, to see if its working correctly

It sounds like U have a bad box. This seems to be the most common problem with them, besides not picking up all the channels.

You need to check supply volts on main micro IC702 on main board of Sony KP-51WS520 TV.
If you have experience of big TV repair then I would recommend to get service manual of TV from any online store and check above said IC supply volts. TV must give error by blinking light in case any problem in drive circuits and if main micro fried, no error signal will be there.

Unplugged my Sony for 36 hours from wall and it solved the problem