You need to download a newer SAP kernel. You will need an OSS ID and password to access http://service.sap.com/patches. And you will need to know what R/3 version, database, and OS you currently use. 

Once you are at the patches website, you will need to click in the navigation tree: 
R/3 -> R/3 + ?Release number? -> Binary patches -> 
SAP Kernel + ?Release number? + 32-Bit -> NT/I386. 

Download everything from the database section and everything from the database independent section. 

One of the files you downloaded should start with SAPCAR and end with a *.exe. 
Rename this file to SAPCAR.EXE and place it in the c:\winnt\system32 directory. 
Go to \usr\sap\<SID>\SYS\exe\run and backup the entire directory to some other directory - 
I usually create a \usr\sap\<SID>\SYS\exe\backup_run directory. Make sure SAP is down, the database is down, the TNS listener is down, and the SAPOSCOL is down before you do this. 

Uncompress all the files you downloaded by opening a DOS box and typing: 

SAPCAR -xvf <file name>.CAR 

All files ending with .SAR or .CAR must be uncompressed. All the extracted files need to be moved to the \usr\sap\<SID>\SYS\exe\run AFTER that directory has been completely backed up. 

Once everything has been downloaded, uncompressed, and moved into the exe\run directory, you can start the SAPOSCOL, the listener and the database services again. And then you should be able to start SAP. If there are any application servers for this database instance, the SAP software will update those kernels on startup. 

If the SAP instance STILL does not come back up, you can take down everything again and restore the exe\run directory with your backup copy. Nothing will have been damaged.

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