is the new power supply working? Sometimes you get a dud. you can check the power supply with a paperclip - google that and you'll get youtube videos demonstrating how to check computer power supply.
The first question a tech support guy would ask is "is it plugged in". By that i mean, check all power connections - go to your motherboard site and make sure you have put the right power connectors on to the right places. You might, for example, have neglected to connect the secondary motherboard power supply, or a mb controlled fan power supply.
When you boot your computer with the video cable properly connected to a monitor that has power - even with no hard drive you should hear a single beep, the sys power led on the motherboard should light up (if your mb has it - most do now), and the bios messages should post to your monitor. You should then get your MB messages that state the bios version and the option to display the post screen (on mine it's press the tab key to watch the bios startup processes) - if you aren't seeing the bios (software loaded permanently on your motherboard) post up when you boot then there's either a problem with your monitor, the motherboard, the power supply, or the power switch.
If you weren't properly grounded against static, you could have inadvertently fried your motherboard as you plugged stuff in. You could also crack the mobo if you pushed too hard - dont wiggle as you insert plugs - pull straight in and out.
The above tip to remove the battery is a good one on some modern motherboards. Some mbs detect power surges and can shut down to protect the system. On these mobos, when you have a surge, they run a routine that shuts the system down and prevents it from getting power. This routine will continue as long as the bios has backup power (the motherboard battery powers your system clock and things like that when you power the computer down, you have to physically remove it to reset these things if your computer wont boot.)