computer stopped working, possibly m'board failure?

my bro was using the computer last night, he said he was just surfing the net and the computer switched off as if the power supply had been cut. it isn't working at all now apart from the green light on the motherboard being steady. Simply, when i switch it on nothing happens.

my specs are:
x2 3800
asus a8n vm-csm
1gb corsair value ram(1 stick)
200gb maxtor sata hdd
480W Xilence PSU

any help is welcome, thanks.

Also, i noticed some scorch marks on my case temp sensor(long wire) which was lying next to one of the capacators.

it is the PSU. i tested it in another machine and it is completly dead. hopefully it hasn't taken any other parts with it but i won't find out for a couple more days.