How to tackle this situation as it may be really frightening
Find your SQL server installation folder it might be in C:\Program Files\Microsoft SQL Server\MSSQL.x\Reporting Services\ReportManager.Here MSSQL.x can be anything where you Reporting Service is installed, generally if you have installed every thing including Notification Service,Analysis Service,Integration Service and DataBase service then it is MSSQL.4
Use the All Programs menu to open the Report Server Status page.
From here you can locate the instance id ie. is it MSSQL.2 or MSSQL.4 etc...
3.Now open the ReportServer.config File and find the line containing <WebServiceAccount></WebServiceAccount>
4. Add IWAM_ComputerName like this <WebServiceAccount>IWAM_ComputerName</WebServiceAccount>
5. Save and then close the RSreportserver.config file.
6. Restart the SQL Server Reporting Services service.