I am having some problems with a friends laptop. It is a HP 6720 about 3 years old.When starting up go's through the normal post screens and then go's onto the microsoft loading screen after about 30 seconds scrren just go's dark. Ive checked ahrddisk and memory and no errors, ive tried system recovery but on recovery screen just sits there for hours on end saying repairing disk errors. As a final measure tried to install windows xp on new harddrive but get error message to do with pci.sys and a long string of numbers. Any help would be appreciated.
The problems you are having may be associated with a hardware issue. HP's don't last that long (usually due to heat damage), which may be the source of your issue. Chances are that the motherboard is shot.
This sounds like a faulty hard drive to me, it is very common in laptops for the hard drive to be damaged due to being dropped when the computer is on. You don’t need to knock the computer much when the hard drive is running to damage the hard drive.
To prove this try Hirens boot CD and run the manufacturer of you hard disk diagnostic software.