Oracle startup error: "end-of-file on communication channel" The Oracle instance I am working with is not coming up after issuing a startup. All I get is the following:

SQL&gt; startup
ORACLE instance started.

Total System Global Area 1.2300E+10 bytes
Fixed Size                  2263088 bytes
Variable Size            1.002E+10 bytes
Database Buffers         3018334336 bytes
Redo Buffers               48056256 bytes
Database mounted.
ORA-03113: end-of-file on communication channel
Process ID: 5038
Session ID: 221 Serial number: 3


For ORA-03113: there shouldn't be any network issues, as this session is logged as sysdba on the machine. And this instance has been working for over two months with no problems.

The oracle service is also running and was able to restart.

Environment: Windows 2008 Enterprise SP1, Oracle 11g R2.

I'd really appreciate any direction and help you could offer to troubleshoot and resolve this issue. 



Here are the details from alerts.log:

KCF: read, write or open error, block=0xf0412 online=1
        file=25 'C:\ORADATAFILES\ORAPROD03\USERS03.DBF'
        error=27072 txt: 'OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 665) The requested operation could not be completed due to a file system limitation'
Errors in file C:\ORACLE\diag\rdbms\ORAPROD03\ORAPROD03\trace\ORAPROD03_dbw1_224.trc:
Errors in file C:\ORACLE\diag\rdbms\ORAPROD03\ORAPROD03\trace\ORAPROD03_dbw1_224.trc:
ORA-63999: data file suffered media failure
ORA-01114: IO error writing block to file 25 (block # 984082)
ORA-01110: data file 25: 'C:\ORADATAFILES\ORAPROD03\USERS03.DBF'
ORA-27072: File I/O error
OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 665) The requested operation could not be completed due to a file system limitation
Sun Aug 19 10:26:42 2012
KCF: read, write or open error, block=0xf04e2 online=1
        file=25 'C:\ORADATAFILES\ORAPROD03\USERS03.DBF'
        error=27072 txt: 'OSD-04008: WriteFile() failure, unable to write to file
O/S-Error: (OS 665) The requested operation could not be completed due to a file system limitation'
Errors in file C:\ORACLE\diag\rdbms\ORAPROD03\ORAPROD03\trace\ORAPROD03_dbw0_5624.trc:
DBW1 (ospiC: 224): terminating the instance due to error 63999


trace file has this error message:

ORA-00449: background process 'DBW1' unexpectedly terminated with error 63999


Now, I understand that the USER03.DBF data file is 
somehow inaccessable. But the permissions on the file are "Full Modify" and nothing else is accessing this specific file, like a backup software or antivirus; this is a dedicated oracle box. 

Given the the file is not being able to be read or write from, what are my options? 
The file size is 27GB, but size on disk is 4GB; I am not sure if this is of any significance. And disk is definatly not out of space.

Autoextend is set at 100MB. And database is about 150GB. Within alerts.log, there were over 50 autoextend notes before the corrupt block error showed up.
O/S-Error: (OS 665) The requested operation could
  not be completed due to a file system limitation


So the windows error 665 is the reason for the error an the error refers to file C:\ORADATAFILES\ORAPROD03\USERS03.DBF.What is the problem with the file? The following article discusses this error message:  What factors can lead to Win32 error 665 (file system limitation)?. If the reason is file fragmentation a patch is available. I know it is to late but maybe a restore will not be necessary in this situation.