Hi NANA ,
Thanks for your reply.
OS is windows NT
DB2 version is 7.1
I have enough space in my home directory ( 2 GB )
I have checked the db2diag.log and I am attaching the part of it here i.e the part of log when the problem started . before that there was no problem
2001-03-20-11.25.26.245000 Instance

B2 Node:000
PID:293(db2ccwrk.exe) TID:292 Appid:
Monitor Server RES_LocatePrfVar Probe:10
DiagData
6462 322e 6462 5f73 796e 635f 7772 6974 db2.db_sync_writ
655f 7469 6d65 e_time
2001-03-20-11.25.26.325000 Instance

B2 Node:000
PID:293(db2ccwrk.exe) TID:292 Appid:
Monitor Server RES_LocatePrfVar Probe:10
DiagData
6462 322e 6462 5f73 796e 635f 7265 6164 db2.db_sync_read
5f74 696d 65 _time
2001-03-21-14.25.10.060000 Instance

B2 Node:000
PID:179(DB2STAR2.EXE) TID:166 Appid:none
oper_system_services sqloStartDB2Service Probe:50
4442 3220 3a20 5468 6520 7365 7276 6963 DB2 : The servic
6520 6469 6420 6e6f 7420 7374 6172 7420 e did not start
6475 6520 746f 2061 206c 6f67 6f6e 2066 due to a logon f
6169 6c75 7265 2e0d 0a0a ailure....
2001-03-21-14.25.10.090000 Instance

B2 Node:000
PID:179(DB2STAR2.EXE) TID:166 Appid:none
base_sys_utilities startdbm Probe:70
DiagData
4442 3220 3a20 5468 6520 7365 7276 6963 DB2 : The servic
6520 6469 6420 6e6f 7420 7374 6172 7420 e did not start
6475 6520 746f 2061 206c 6f67 6f6e 2066 due to a logon f
6169 6c75 7265 2e0d 0a0a ailure....
2001-03-21-14.47.53.010000 Instance

B2 Node:000
PID:210(DB2STAR2.EXE) TID:156 Appid:none
oper_system_services sqloStartDB2Service Probe:50
4442 3220 3a20 5468 6520 7365 7276 6963 DB2 : The servic
6520 6469 6420 6e6f 7420 7374 6172 7420 e did not start
6475 6520 746f 2061 206c 6f67 6f6e 2066 due to a logon f
6169 6c75 7265 2e0d 0a0a ailure....
2001-03-21-14.47.53.040000 Instance

B2 Node:000
PID:210(DB2STAR2.EXE) TID:156 Appid:none
base_sys_utilities startdbm Probe:70
DiagData
4442 3220 3a20 5468 6520 7365 7276 6963 DB2 : The servic
6520 6469 6420 6e6f 7420 7374 6172 7420 e did not start
6475 6520 746f 2061 206c 6f67 6f6e 2066 due to a logon f
6169 6c75 7265 2e0d 0a0a ailure....