Question : Windows 7 BSOD STOP: c0000221 Unknown Hard Error ntdll.dll

Hey guys

I got a PC here what has a pretty severe problem. It all started up when the screen flickered couple of times and then it froze. Then few times it was just restarting continously and coming up with options for Safe Mode and so on. Then I was asked to have a look at that PC. When I saw it for the first time it came up with Launch Startup Repair / Start Windows Normally options. I chose Launch Startup repair and it ended up with a BSOD and the following message:
STOP: c0000221 Unknown Hard Error
 \systemroot\system32\ntdll.dll
The same message comes up when I try to boot that PC from a Win7 installation disk. I could actually get into Safe Mode though. From there I have started sfc /scannow what came up empty. Also I have managed to get to Normal Windows couple of times but it usually ends up crashing following loads of error messages.
Current situation is that it won't boot from DVD (BSOD), Safe Mode and Normal Mode won't start (stayes on black screens) - so pretty much stuck.
Few specs about the PC:
Windows 7 x64
4GB HDD
500GB SATA HDD

Any help would be appreaciated.

Answer : Windows 7 BSOD STOP: c0000221 Unknown Hard Error ntdll.dll

Spanning tree should be enabled by default unless you have disabled the protocol; you should also disable any unused ports that are not being used (This will somwhat stop mischief); there are other mechanisms (Layer 2 attacks) you should consider (CDP, Mac Spoofing, Root Guard, Broadcast suppression, etc). There are many tools available that can bring down a network. Do you have a network diagram? Do you have STP disabled?

Billy