I have a compaq presario se1020nx and i transferred the computer to a new desk when unplugging it the green led light on the back started flashing and has been now for a week and it wont power up at all what could it be

The Green LED light flashing on the back of the Power Supply, indicates the Power Supply is bad.

Weak voltage power rail.

I know it sounds weird, since you all you did was to move the computer to another desk.

You may wish to try a couple of things before purchasing a new Power Supply.

1) Computer unplugged from power, open the computer case. Is it dirty inside? Dust, dirt, hair, etc.? ('Gunk')

Use a can of compressed air for computers, and clean the inside of the computer out.
Attach the plastic 'straw' to the can of air's nozzle, break off the lock tab on the top of the trigger.

Start at the top inside Left, and go across to the Right.
Spray air like a painter using a paint sprayer.

Squeeze the trigger in all the way as you start. Upon reaching the other side, let go of the trigger.

Drop down a space, and make another row across.
(Spacing is up to you. You can judge spacing by the 'gunk' removal)

Keep dropping down, and going across in rows.
Upon reaching the bottom, tilt the computer case top towards you slightly, and b low the gunk out of the bottom of the case.

Pay special attention to the Processor Fan, and the finned Heatsink sitting under the fan.

Use SHORT bursts of air on the fan.
(Squeeze the trigger in all the way, let go quickly.
The fan is only designed to spin so fast. Spinning it faster than it was designed for, can lead to premature failure of the fan's bearings)

Hold the can of air with one hand, hold the plastic straw with the other hand.

Stick the straw in the ventilation holes of the Power Supply's case, from the inside of the computer, and rid as much 'Gunk' out as you can.
(If you do not hold onto the straw, it can shoot off of the can, and wind up inside the Power Supply)

2) Reseat the Ram Memory.

Even if it looks as though the ram memory modules are seated, it would behoove you to remove them, and reseat.

All it takes is a small bump, and the ram memory module/s will not have a good contact.

Reseating the Ram Memory module/s ('Stick/s')

http://h10025.www1.hp.com/ewfrf/wc/document?docname=bph03886&cc=us&lc=en&dlc=en&product=403789&tmp_track_link=ot_search

Scroll down the page to view the animated GIF's.

This is HP Support > Compaq Presario SR1020NX desktop computer > Support main page,

http://h10025.www1.hp.com/ewfrf/wc/product?product=403789&lc=en&cc=us&dlc=en&submit.y=6&submit.x=7&lang=en&cc=us

Click on > Manuals
In the Manuals list click on > Parts Replacement Instructions.

(10.36MB in size, PDF file. Allow the file to fully download before perusing through it)

Shows you how to replace the Power Supply.
Have any questions as you proceed, come back here, and state in a Comment, and I'll walk you through it step by step.

The Power Supply used is an ATX form factor.

The type of Power Supply used in over 85 percent of PC desktop computers.
very readily available in a multitude of places.

(Average cost for a decent one is around $30)
Need help in finding an ATX power supply, let me know in a Comment.

Regards,
joecoolvette

The power supply is bad.