What exactly are you using for a psu?
A GTX450 wants a 400w psu and a 6 pin connector.
A 9500GT wants 350W.
If you have a less capable psu, you would have those issues.
Or, if your psu is a cheap one of poor quality, it may not deliver all the advertised power, or may not deliver it on the +12v rail where it is needed.
I believe it is a 550W Thermaltake W0330RU, but I'm not too sure.
Here's a image of it.
Enjoy the dust.
Also, after I removed the 9500GT, the mobo wouldn't post.
I had the same issue with my old MSI mATX mobo that I had a week ago, so this isn't a motherboard issue for sure.
Also, for some reason, the 3V rail seems to be very high when I first turn it on. But then it goes down after Windows starts.