My compaq evo does not boot. The power supply fun does not is not work. The processor does not work too. Red light blinks infront of the PC. There are two green lights on the motherboard

bad motherboard

How many times does the red light come on ? It should blink a number of times, then go off for a little while, and start blinking again. The number of blinks within each cycle will help you find out what is wrong:
Number of 1-second red LED blinks followed by 2-second pause, then repeats:
2-processor thermal protection activated
3-processor not installed
4-power supply failure
5-memory error
6-video error
7-PCA failure (ROM detected failure prior to video)
8-invalid ROM, bootblock recover mode
(http://h18000.www1.hp.com/products/quickspecs/productbulletin.html#spectype=worldwide&type=html&docid=11632)

Power Supply.

Weak voltage power rail, or more than one.

(There are three power rails for the Power Supply used in your computer;
1) The 3.3 Volt power rail
2) The 5 Volt power rail
3) The 12 Volt power rail.

Wires with Orange insulation carry 3.3 Volts
With Red insulation carry 5 Volts
With Yellow insulation carry 12 Volts.

Each wire is connected to one power rail in the Power Supply.
{All Black wires are Ground wires}

The Power Supply in your computer is an SMPS. Switched-Mode Power Supply,

http://en.wikipedia.org/wiki/Switched-mode_power_supply )

I don't know what form factor your Power Supply is because you didn't state which model it is.
Small Form Factor (SFF)
or
Convertible Mini-Tower
or
Ultra Slim Desktop

Post additional questions in a Comment. Also state what model your Compaq Evo D510 is.

Regards,
joecoolvette

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You may need to replace one of your ram cards. Take it to a pc shop and ask them to perform a "memtest"

This power supply is quote HP, "250 W Power Supply (PFC)". Almost any power supply will provide that much power. The problem is in a mini tower, the shape has to be matched and that limits you generally to the manufactures PS. Here is one that will replace yours.http://www.codemicro.com/store/product/243891002/New

If this answers your question, I'd appreciate 4 thumbs. I do this for fun and do not get paid.
Jim

i think the problm with motherbard or fan please check

4 blinks, 1 second apart is a power supply overload. Have the power supply replaced if you haven't added any additional hardware lately. But also make sure your hard drive isn't bad and pulling an overload of power. it's rare, but I have seem that happen on some western digital hard drives.

Check your Bois and go to in boot sequence option set that on default

it all depends on the number of flashes , pause, repeat.
Since the problem did not indicate any beeps her is the following info


Power LED blinks RED 2 times, one every second, followed by a
2-second pause. = Processor Thermal Protection Activated


3 blinks 1 second apart = Processor not installed (not an indicator for a bad processor).

4 blinks 1 second apart .= Power Failure (power supply is overloaded)

Other possibilities are:
5 blinks 1 second apart No memory
6 blinks 1 second apart No graphics
7 blinks 1 second apart System board failure (detected prior to video)
8 blinks 1 second apart Invalid ROM