The screen goes black,after replace my friend's ddr333 256mb with ddr400?

The chances of this being related to your memory are very, very small. If he is still under warranty with HP, he should request a new motherboard. If not, reset his BIOS to defaults using jumpers as directed in his user manual, see if that fixes it. Otherwise, change out the graphics card, being sure not to confuse PCI and PCI-X. I'm always careful with Motherboards, as a failure of one device on it usually foretells the failure of all other devices, since they were created at the same time with about the same level of quality. He should consider a new motherboard or system.