When i push the power button nothing happens

SOURCE: Dell Dimension 4600C will not power up

Sounds like the power supply is faulting. If not it is your mother board that has failed.

SOURCE: Not the power supply!

Hi

To help troubleshoot a problem, Dell Dimension 5100 has four diagnostic lights labeled "1," "2," "3," "4" on the front panel. When the computer starts normally, the lights flash. After the computer starts, all four lights lites solid green. The power button also lites solid green. If the computer malfunctions, the color and sequence of the diagnostic lights as well as the power button helps identifies the problem.

First, disconnect the power cord and remove all connections (Keyboard, Network, Mouse etc) as well as optional PCI Cards. Connect up the power cord (Monitor as well) and try powering the PC.
Check the diagnostic lights/system lights color and sequence and check the link below for more info (Assuming you have another system that can access internet)
Diagnostic Lights - http://support.dell.com/support/edocs/systems/dim5100/en/sm/tshoot1.htm#wp1120147
System Lights - http://support.dell.com/support/edocs/systems/dim5100/en/sm/tshoot1.htm#wp1114432

Reply with lights color and sequence as well as any beep codes and I will respond at best effort.

Mike

SOURCE: DELL DImension does not boot

http://dell-driver.driveray.com/dell-drivers/s_329_1.shtml

SOURCE: computer will not turn on at all. Dell Dimension 5100 desktop

I would unplug the power supply from the motherboard, wait a little while and then plug it back in.
Try to power everything back up and it should come up.

I am assuming you are getting a light on the motherboard that indicates power is being supplied?

SOURCE: Will not power up

try re-setting the BIOS by using the clear CMOS jumper on the motherboard. If that does not work then remove the memory dimms, cd-rom drive, hard drive, floppy drive and any PCI components. After that try the computer and see if you at least get a post-up screen. If you do then re-connect each component until the post up screen stops again and that is your problem component. If not then your motherboard is bad.