Spec is

E6550
SG33G5
300 W power supply PC-50
Crucial 2 x 1 GB DDR2-800 MHz
Vista Business
Samsung DVD-RW
Hitachi 500 GB T7K250
Seagate 7200.10 500 GB
eVGA 7800 GT 256 MB

Since Shuttle PSU doesn't have the PCI-E 6 pin power connector, you have to use the power connector which has one end that connect to videc card (vcard), and the other end with 2 male power connector (like legacy IDE HD power connector). Lets call this 2 end connectors A and B

And on the other hand, Shuttle PSU has one end that has 2 female power connector, lets call it C and D

This is what happened

Strange thing is that if I connect A to either C or D, the PC boots up (that means the C and D that comes from 300 W Shuttle PSU has power), BUT if I connect B to either C or D, it won't boot up. If I connect both, meaning either A - C, B - D or A - D, B - C, PC won't boot up either.

Therefore the following table
A - C [OK]
A - D [OK]
B - C [not OK]
B - D [not OK]
A - C, B - D [not OK]
A - D, B - C [not OK]

All this scenario happens with all peripherals powered (meaning the 2 HDs + 1 DVD drive are powered). I also took out the power to DVD drive when I first tried to figure out, thinking that maybe the PSU is not powerful enough, but still, it won't matter as it comes down to above combo so I think it's not the PSU.

Anyone can tell me what's wrong?