Computer starts to power up, two beeps then nothing and wont come on

SOURCE: Computer wont start

The beep codes are related to hardware issue with your computer. Could be the RAM, video card or the motherboard. However to help you better, we would need to know the model number of your computer and preferrebly the BIOS manufacturer

SOURCE: HP Compaq dc5000

Your motherboard is complaining. Try reseating the memory and rebooting. If that doesn't help, you should consider another motherboard. You could probably get away with just replacing the CPU, but that's not too cost-effective. Its just time to upgrade!

SOURCE: Installed new DIMM memory in Compaq D510 CMT - puff of smoke

Here's a full list of the POST beeps for your computer:

http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c00704816/c00704816.pdf

That flashing numlock and beep pattern says there is no system memory. When you let the smoke out before it might have been fatal for something. It could be the memory itself is dead, or something could have been damaged on the system board that is keeping it from detecting memory. The only way to know for sure is to try another stick of known good memory.

There's also the possibility you used the wrong kind of memory when you added the new part. Here's a link to the hardware guide for the computer:

http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c00706221/c00706221.pdf

You can use the information to be sure any memory you get is supported.

Hope this helps you. Good luck getting the computer running.

SOURCE: Four beeps wont turn on, Dell 4700

The four beeps usually indicate a memory problem and it won't pass it's Power On Self Test. Try reseating the memory sticks, or, if you have two of them, take one out and try to start the machine and then swap them.
If this doesn't solve the problem, you most likely have a bad motherboard.

SOURCE: computer wont boot hear one beep from motherboard over and over

If your power supply is bad, there is typically a much cheaper way to fix it rather than purchasing a new one.

If you know a little about electronics or know someone who does have them open up the power supply and check the capacitors. Often times when a power supply goes bad its the result of capacitors going bad.

If you notice on the ends of any capacitors a brownish/whitish discharge or "bulging" then the capacitor has gone bad.

A new one typically cost less than a dollar and replacing it is fairly easy if you know how to solder.

Let me know if you have anymore questions and hopefully if this is the case you can save some money.