Bad Power Supply. Weak voltage power rail.
Has enough power to light LED lights, and maybe spin fans, but not enough to turn the Processor on.
1) ALL of the LED lights on at once use less than 1 Watt of power.
2) EACH fan uses 2 to 3 Watts.
3) A typical Processor uses 51 to 125 Watts. Depends on what Processor it is.
The Compaq Presario SR2013WM desktop computer, comes with an AMD Athlon 64 3800+ processor, that fits in a Socket AM2.
Can use up to 62 Watts.
No Processor operating, no computer.
No computer operating, No Signal to the monitor. (No video signal, or also known as No VGA Signal)
The Power Supply used is just one of the common ATX form factor power supply's.
Used in over 80 percent of PC's out there, and readily available.
(ATX size of the power supply case, is approximately 5-1/2 inches Long, 3-1/2 inches Tall, and 6 inches Wide)
It is 250 Watt, and a generic model. Probably made by Bestec, Delta, or HiPro.
(You can use a larger wattage Power Supply with NO problems.
A computer ONLY uses the power it needs, and NO more)
A) The ATX main power cable is a 24-pin ATX main power cable. All of the new power supply's have an ATX main power cable, where the connector can be used as a 20-pin, or 24-pin.
B) Uses a 4-pin ATX +12 Volt power cable.
C) Past the two power cables above, just make sure the Power Supply has a SATA power cable, (For the SATA harddrive), a Floppy Drive power cable, (Used for the Card Reader), and enough 4-pin standard Peripheral power cables.
(Misnomered as 'Molex')
3) Typical 24-pin ATX main power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain24
4) Typical 4-pin ATX +12 Volt power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#atx12v4
5) Typical SATA power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#sata
IF, the SATA harddrive has a provision for using a 4-pin standard Peripheral power cable, AND a SATA power cable, ONLY USE THE SATA POWER CABLE.
If you use both you will burn up the SATA harddrive.
6) Typical 4-pin standard Peripheral power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#peripheral
Have questions regarding the above, or need recommendations on a Power Supply, please post in a Comment.