PSU/mobo compatible???

So I tried putting this motherboard, Biostar A880G+ in a Dell Dimension 2300.
What I've already upgraded also:
RAM to DDR3
adapter to turn IDE HDD into a SATA connection
CPU to AMD Athlon II X2 245 Regor 2.9GHz AM3 65W Dual-Core
stock heatsink from an AMD Phenom II x6 1090T

Unfortunately, the board has a 24-pin socket for psu connection, whereas the Dell psu has a 20-pin connector. All I've read so far is that this shouldn't be a problem, "unless it's a Dell psu-" then maybe there will be a problem. I hooked everything up, and it wouldn't power on. Literally, I pushed the On button, and absolutely nothing whatsoever. It didn't even try to power on. Is there anything else I could check? What can I do???

There are issues between some Dell power supply units and the standard ATX motherboard and you probably need to buy a Dell to ATX Power Supply Converter as pictured here:

Adapter for Dell Power Supply

More excellent information here:

InformIT: Dell proprietary (non-standard) ATX design > Dell proprietary (non-standard) ATX design

It would appear that trying to match a non-Dell PSU with a Dell motherboard (and vice versa) can damage your motherboard and is Dell's way of ensuring you have to buy Dell PSUs if you want to upgrade your Dell computer.

I know this to be true because earlier this year I tried to upgrade the graphics and power supply on a Dell XPS 8100. The new power supply had a 20-pin connector while the Dell motherboard had a 24-pin socket.

When I switched on there was no power so I put the old power supply back in and returned the new PSU and graphics card for a refund.

The Dell from then on ran OK, but the CPU cooling fan cut in constantly so I contacted Dell about the issue who then replaced the motherboard, CPU and cooling fan. Coincidence or what? It would seem the new power supply had fried the motherboard.

I would cut the middle man out and buy a suitably rated standard ATX PSU (assuming that the current Dell one is a standard sized one), as PSUs included by many manufacturers such as Dell have only sufficient power capacity for the hardware that the system comes with.

Come to think of it, I did notice that when I was looking for the wattage, I didn't see ATX labeled anywhere. Although, there isn't much labeled on it at all. =/ So, SeaVixen, do you think that converter that jeepmann suggested will work for now?

It's 250W, and here's the peripherals:
cpu (65W)
1 HDD 7200RPM (tho with my luck lately I expect this to turn out shot --_--")
1 DVD drive 16x
1 CDR/W drive 40x
Biostar motherboard (can't find any power requirements)
2 GSkill 2GB DDR3 1333MHz
80mm fan 1800rpm
front 2 usb ports & headphone jack are unconnected
Do you think I could I get away with the 250W & just an adapter for a bit longer???

Ugh this was supposed to be a cheap way to boost my lil sister's computer, but with it being sooo old & the incompatibilities with Dell, the numbers keep going up.
Nonetheless, thanks for all the info, folks! :)

Nevermind, I checked the prices and the adapter is just as much as a new 350W psu! lol
Also ran the specs through a power calculator & came out with 272W, a suggestion of 299. 350 should keep well. :)

Well, a little bit. $15 for 350W power supply is pretty great though. =)