After replacing power supply computer doesn't boot

[Aaron4021]

  Just recently my power supply started making an aweful noise because one of the fans was going.  I turned the computer off and removed the power supply and all of the connections, I replaced the power supply and now when I tun on my computer the lights go on but the monitor won't turn on, if I press the power switch on the monitor the monitor will start to power on and then shut off right away.

 Can anyone help me with this?  My old power supply was a 550W and the new one is a 400W (though that shouldn't matter).  When I was checking fans for noise I thought it was the CPU fan, so I took it out rather harshly (the way it was held on made it very hard to remove), is it possible I knocked it out of place or wrecked it?  Orrrr... did I just forget to plug one connector in, I plugged the mobo connector, the other 4 pin connector on the mobo, the floppy power, the disc drives and hard drive 4 pins and  the ribbon cables for the disk drives and hard drive.

[Aaron4021]

  I am very sorry for the spelling mistakes and typos, I forgot to use spell check and unregistered users can't edit posts.  (and the keyboard on this computer is horrible)

[patio]

If the CPU fan got damaged in removal it's possible it is not letting the board power up fully...this is a built in fail safe to avoid damage to the CPU.
Does the CPU fan turn at all ? ?
Are you getting any beeps when you power up...if so how many and how long ? ?

patio.  

[smelly_Cat]

If you dont see the video card at start up .  It means the CPU aint turning on or its fried.  if you have an old Power supply try it to see if it will boot with that.
Maybe your new PS is frazzed.  I've heard of new PS's being bad.  SC

[Aaron4021]

  I tried removing components one by one out of the computer, and I don't think the power supply is the problem because the computer does the exact same thing with the old and the new power supply.

the monitor doens't turn on when i boot no matter what I do.
 Without the video card, the computer still boots nothing (though everything spins).
 with only the mobo power connector it does the same thing.
 with every power cable it does the same thing (except the drives that are plugged in start)

 The CPU fan is still going, but I don't think it's going at full power.  I think the problem is with my cpu, I think it's damaged.