My computer can't boot up any more. I found it dead when coming back from work. I completed the 2 day downloading this morning using 56K modem. I disconnected the internet and went to work. When I was home, it seemed the computer is locked. can't reboot using Ctrl+Alt+Del(task manger). can't work using reset button. Only way is to unplug the power cord. I rebooted it and found still can't boot up. The computer even made noise from CD-rom drive. I tried to reboot it and found I can't. I unplug the power cord and re-plug and boot. Other noise come from somewhere (modem or hard drive???). I hope somebody could help me out. I am wondering if the motherboard is burned up, or if the power supply is not good. Here is my specification.

Mobo: MSI 6340M (can't overclock)
CPU: Duron 750
Power supply: 200 Watt ATX power supply
DVD-Rom
Nec CD-RW
OS: Windows XP
Memory: 256M + 128 M(different brands)
Hard Drive: 15G(2 partitions: 5G & 10G)

My computer was working OK before, and I never shut it down. I installed XP serveral times. Any response is appreciated.

Regards.