urgent: Back up Problem Serious

This isn urgent and Important!!

I am using SAP 2005B PL39. I am trying to take the back up but the back up is not being taken. The database file is of >2GB. The back up of OEC Computers is being taken but to the utter surprise the BU File is not present. I deinstalled and then Reinstalled SAP, but with no results.

Actually, the temp file is showing the BU Back up but that gets vanished suddenly and then the zip file in the back up folder is having no BU File. This also is happening only for SBODemo_India Database.

Can any one please suggest me the reason or a suitable suggestion.