HP Pavilion a1615.uk fails to boot

[Mahakala]

I have an HP pavillion a6115.uk. It will not boot windows vista.

After switching on and getting pre boot screen the following info is on screen in blue screen. The following info is on screen briefly.

stop coooo 221 unknown hard error.

\systemroot\system32\ntdll.dll.

Collecting data for crashdump.
initialising disc for crashdump.
beginning dump of physical memory.
physical to disc.
dumping memory.

Then there is a brief rapid countdown.

Then it goes back to the pre boot screen, then to error recovery screen.
Unfortunately I didn't get boot discs with PC

Please help!

[Phalguni88]

Ntdll is a common error in Windows and there are number of reason why it is caused. The first easy thing you can do is boot in recovery mode and copy paste the missing dll files. You can find the file from web also. Sometime it is also caused due to corrupt hardware. So try to disconnect any hardware like printer or any other stuff connected to your pc. Then check back. One more thing you can try is removing your system ram and then putting it back in another slot.