Alright your system is very advanced so the steps to install all the devices is crucial.
If you think it is your hard drive get the manufactor software and run a diagnostic on the drive, this software<maxblast,seagate tools,wdd,dft test> will tell you if there are any errors on the drive. Go to the manufacturors web site and they will have the software.
Next like on some of the other replies, the 9800 ati cards need to have the drivers and software installed before installing the card itself.
I think your computer is fine, I am a computer technician and have been giving computer diagnostics for years, and your computer sounds like a quite advanced setup, yes getting it to work anybody can do, but loading the O.S, drivers, and having your CMos setting's all correct is difficult.
So first thing backup your data and format your drive, pull all un needed cards out of the tower, and put the other video card in for just the setup, and put in the 9800 later.
After you have the drive formatted go into bios, and set it to load defaults.
Reboot and spend about an hour making sure you have all the settings right, even if you think there right double check. Especially Memory/cache/cpu/ settings. If not set correctly the hardware and the motherboard cannot communicate correctly and will always be running under it's capabilities.
Next load Windows if your not using XP Professional get a copy, because the 64 bit architeture technology cannot run correctly on XP home, or any other version of windows except for XP64.
Load windows, and after your finished load all the Windows Updates, till the last one.
But if your still having boot problems pull the mobo, out of the case and "bench" the hardware out side of the case. Grounding issues will cause a computer to start but stay idle and not totally go through the boot process. Make sure you unplug the power supply from the mobo, If you had any shorts this will clear the running elecrtrical current running through your computer. If it does boot get into the bios, and go to boot device settings, which you will want to set the first boot device to CD, Oh yeah if you like to keep cd's in the computer when it's booting, I have seen dozens of times this being the reason for no bootup or very slow performance. I hope this helps, If in the end of all this It still isn't working call the manufactuor of the motherboard, and try to RMA it, and get technical support from them, What type of board do you have? Get Asus if this one is bad, the rest are crap.