Long-ish first post, sorry 
My computer was working fine a few days ago, but the mouse and keyboard kept freezing up, the only extra thing added was my sons MP3 player charging from a USB port. So I powered down and left it off for a bit, went to turn it back on and had a No signal display on the monitor, figured after awhile it was just the VGA connection so I decided to get a new mobo. (the old mobo was a biostar mini ATX, AMD Athlon 64 3500+, 2G RAM, onboard video) Got a new mobo (the brand slips me, right off) that had a AMD sempron 3000+ on it, socket 754, so I replace that CPU with my old one, toss in my vid card that I was never able to get to work on the biostar board and booted up, everything worked fine, save the USB ports weren't working at all, double and triple checked the connections, noticed that when the system powered up, the Ethernet port light would flash on and then back off, no power to it at all it seemed. So I replaced the CPU with the sempron and it booted up fine, still no power to the USB or Ethernet ports (normal keyboard worked, however). Shut down again to try and figure out the problem and upon restarting, once again, im back to having no signal to the monitor, the only thing I can figure is its the PSU? I was running a 500W PSU but the fan stopped so I switched to the 450W that came with the Case (no name brand, case was a XION). So could it be the PSU, after having tried more than one CPU, Mobo, and monitors, cables, just trying to figure out th is problem so I can get back online, thanks for any help : D
My computer was working fine a few days ago, but the mouse and keyboard kept freezing up, the only extra thing added was my sons MP3 player charging from a USB port. So I powered down and left it off for a bit, went to turn it back on and had a No signal display on the monitor, figured after awhile it was just the VGA connection so I decided to get a new mobo. (the old mobo was a biostar mini ATX, AMD Athlon 64 3500+, 2G RAM, onboard video) Got a new mobo (the brand slips me, right off) that had a AMD sempron 3000+ on it, socket 754, so I replace that CPU with my old one, toss in my vid card that I was never able to get to work on the biostar board and booted up, everything worked fine, save the USB ports weren't working at all, double and triple checked the connections, noticed that when the system powered up, the Ethernet port light would flash on and then back off, no power to it at all it seemed. So I replaced the CPU with the sempron and it booted up fine, still no power to the USB or Ethernet ports (normal keyboard worked, however). Shut down again to try and figure out the problem and upon restarting, once again, im back to having no signal to the monitor, the only thing I can figure is its the PSU? I was running a 500W PSU but the fan stopped so I switched to the 450W that came with the Case (no name brand, case was a XION). So could it be the PSU, after having tried more than one CPU, Mobo, and monitors, cables, just trying to figure out th is problem so I can get back online, thanks for any help : D