Yes. A few.
1) Sometimes we inadvertently bump wires loose, when we are replacing hardware.
The Front of your computer is the Front Panel.
The area of contact pins on the motherboard, that the main wires from the Front Panel go to, is the Front panel header.
Two of these twisted pair of wires are for the Power On switch.
Are they connected tightly to the pins in the Front Panel header?
2) There is a main power wire that comes from the Power Supply, and plugs into the motherboard.http://www.the620guy.com/images/ebay/2011-11-21/Acer%20AcerPower%20S280%20CelD%203-06GHz%203.JPG
(You can click on the photo to enlarge)
The Black long connector at the top is for a Floppy Drive.
Under it the Blue long connector is for the Harddrive.
Under it is the White long connector for optical drive/s
(I may have the blue connector, and black connector, functions reversed. Blue IS supposed to be for the harddrive, usually)
To the left of them, is the whitish long 20-pin ATX main power connector on the motherboard, (20 socket holes), that the 20-pin ATX main power cable plugs into.
General example of a 20-pin ATX main power cable, and it's respective connector on the motherboard,http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain20
In the middle photo observe the whitish connector. Looking close observe the Lock on the side.
Viewing the photo to the left, observe the Tab on the motherboard connector.
When the hooked end of the Lock is over the tab, on the motherboard connector, the power cable is plugged in properly.
Is the 20-pin ATX main power cable plugged in correctly?
Everything is chilly?
3) Then it's time to bypass the Power On switch, and see if the problem is the switch, or the Power Supply.
Yes, a Power Supply can go t1ts up all at once.
Bypassing the Power On switch, has nothing directly to do with the switch. No insulation of wires is cut.
Your Power Supply converts AC electricity from your home, or business, into LOW DC voltages. The shock hazard is contained inside the metal case of the Power Supply.
You will be dealing with 5 Volts DC.
In comparison two D cell flashlight batteries store 3 Volts DC.
A jumper wire goes down into the BACK, of the 20-pin ATX main power cable's connector.
Plugged in just like the photo to the far right in the Playtool link.
Power Supply plugged into power.
Goes down into the socket hole, RIGHT NEXT TO the existing wire, already in the socket hole.
Right next to the insulation of the wire, and down in the socket hole far enough, that the jumper wire touches a metal terminal.
All the wires going down into the power cable's connector, end in a metal female terminal,http://www.molex.com/molex/products/datasheet.jsp?part=active/0002081202_CRIMP_TERMINALS.xml&channel=Products&Lang=en-US
You are seeing the tips of the female metal terminals, in the middle photo of the Playtool link. (In the Molex link above, the tube shaped end to the right, is what you are seeing the tip of)
The jumper wire will be touching the crimped side of the metal terminal, as shown to the left in the Molex link. (Terminal is shown un-crimped)
Make SURE the jumper wire touches the metal terminal.
The preferred jumper wire is a straightened out paperclip, and bent into a U-shape. The top of the U, is wrapped a few times with black plastic electrical tape. This taped area is for your fingers, and thumb to hold onto.
U-shaped jumper wire upside down, it has two 'legs'.
It is these 'legs' that go down into the socket holes.
Observe the photo to the far right, in the Playtool link.
The Green wire is the Soft Power On wire. Abbreviated as PS_ON.
One leg of the jumper wire goes down into the socket hole, with this Green wire.
The other leg of the jumper wire goes down into ANY socket hole, that has a Black wire in it.
ALL Black wires are Ground wires.
The contact made is no more than 2 seconds.
(The Power On switch is a Momentary Contact Switch)
IF, the Power Supply comes on, you have a bad Power On switch,http://www.directron.com/atxswitch.html
IF, the Power Supply does Not come on, you have a bad Power Supply.
For additional questions please post in a Comment.