Hi sorry for the lengthy post but I wanted to be as descriptive as possible. Ok so I replaced my psu a couple months ago with a cheap $20 psu and of course it crapped out in a matter of months. So I bought a new better one and accidentally plugged in the power plugs backwards into the cd and dvd drives. What made me aware of the problem was the cd drive started smoking! So I unplugged everything and made sure the connections were right, threw out the cd drive and rebooted the computer. At first the system would boot fine but kept restarting halfway through loading Windows XP. The dvd drive light would come on but not respond to pressing the eject button. I tried going through some of the recovery start ups at the start screen but nothing fixed it. So I went to BIOS and told it to ignore the dvd drive and tried again, but to still no avail. I then unplugged the dvd drive and tried again. Now nothing happens! All the fans are running fine but the hard drive does nothing and the monitor says no signal even the power button LED doesn't light up. I know I did a big no no but was wondering if I anybody has any pointers. I've tried unplugging everything except for the basics (monitor, fans, mouse, keyboard, ram) but that didn't help. I've read on another forum about unplugging the cmos battery and trying again but I'm at work so will have to try that later. The computer is an Hp Pavilion a8 something (i'll look it up later) with an Intel Pentium 4 chip.

You MUST always unplug the PS or otherwise remove the AC power to it whenever you make any connections or component changes inside the computer case. You can easily damage the PS or the mboard or anything connected to it if you don't do that.
ATX mboards are always being powered by ATX PSs in some places even when the computer is not running as long as the PS is receiving live AC.

It's a huge risk to use an el-cheapo PS. They are a lot more likely to damage the mboard or anything connected to it when they fail.

"...accidentally plugged in the power plugs backwards into the cd and dvd drives"

How did you manage that? The shape of the power connectors plastic shroud fit in the socket on the drives only one way - it is quite difficult to force them in upside down.

In any case, the DVD drive should eject or retract it's tray when you press it's button regardless of whether the data cable is connect when the computer is running.
It has also probably been instantly trashed by you plugging in the power connector backwards, if not right away, the instant you tried to boot the computer after that, despite the fact you noticed no smoke from it.
If you can't get the computer to boot, try it connected to another computer or try a known good PS connected to this mboard (the PS must have a significant load on it - e.g. at least the mboard - in order for the PS to start up).

"All the fans are running fine but the hard drive does nothing and the monitor says no signal even the power button LED doesn't light up"

That is either the symptoms of a damaged PS, more likely, or a damaged mboard.
Damaged PS often partially work but the mboard cannot fully boot.

Failing power supplies are common and can cause your symptoms.
Check your PS.
See response 4 in this:
http://www.computing.net/hardware/w...

Do you have another known good PS you can try?
You may have damaged your newest PS when you plugged in the power connectors backwards.

If a known good PS allows the computer to boot normally, you just need to replace the PS again.
If the system still won't boot you have probably trashed the mboard, or the cheap PS failing damaged the mboard but it took a little time to fail.
Usually the ram, cpu, and hard drive(s) are still fine if the mboard has failed. The cards in slots may or may not be damaged, but usually they aren't.

Thanks for the advice. I did have the computer turned off and unplugged from power when i installed the psu and attached all the components. i don't know how i plugged the power connectors in backwards, they felt like they went in fine when i plugged them in. I'll have to check the drives and connectors to see how it was so easy. I think i do have an extra psu around i could use to test. Thanks and i'll let you know how it goes

"they felt like they went in fine when i plugged them in."

If they were backwards/upside down they would have been really difficult to plug in.

It could be you had the power connectors the right way but you had AC power to the PS when you plugged them into the optical drives.
I used to assume plugging in a drive in that situation couldn't do any harm, until one time when I got a tiny spark while plugging in a hard drive and that it turned out had instantly killed the PS (it definately wasn't a static discharge, and it was plugged into a power bar protected against power spikes and surges).
It could be something like that intially damaged the PS, and the PS in turn malfunctioned such that it damaged the optical drives. If it did that it may have damaged the hard drive(s) too.
Or it could all have been after effects of the cheap PS failing and damaging them board and/or the optical drives etc.

I checked and I did plug them in backwards and messed up the connectors. I tried a few things and still nothing works so i think I'm going to take the psu back and try a new one if that doesn't work it looks like i'll be looking into a new computer :(

The PS warranty doesn't apply if you hook it up wrong. If you can see the power connectors are damaged so can the seller.

Well the store let me exchange it for a new psu but i got the same resutls. I'm pretty sure I damaged my motherboard. Crap. Thanks for your help!

If you're interested, if you supply the exact HP Pavilion model number, I may be able to determine which mboard it has (HP did not make it), and if so, there are often used mboards that were used in brand name systems on the web you can buy for a reasonable price. You may be able to use all your componnents on it and have a working computer again.

But in this case, before you buy and replace the mboard it would probably be a good idea to try connecting your hard and floppy drives to another computer to see if they're okay first, because they may be fried too because of what you did - if they're fried, there's a strong possibility the cpu and ram and cards in slots are also fried.
If it is IDE the hard drive should be connected as slave on either IDE, or as master on secondary IDE, ands/or whatever way you connect it, don't set your bios boot order settings to boot from it on the other computer.
You only need to determine whether it works and the data is intact.
If it's SATA, don't connect it or set your bios boot order settings to boot from it on the other computer.
It won't boot all the way into XP if you boot with it on the other computer if the mboard is more than a little different - that's normal.