Linked server from MSSQL to Oracle Issue
If you're able to select the 'Oracle Provider for OLE DB' option in the "Provider" dropdown, then I'd suggest trying the following (via the GUI):

Product Name: ###.###.#.###:####/SRV1

Data Source: ###.###.#.###:####/SRV1


Where ###.###.#.###:### is your Oracle Instance's IP Address (with standard 1521 or 152# port), and SRV1 is your Service name.

Just make sure the ORACLE user you're using to get in is correct in the "Security" section.

This option allows you to bypass the TNSNames file if you want to confirm that there's a connection (TNSPing is my go to, just like Gerald H. Pille said in the comments above).

Or if you want to go about it via T-SQL:

EXEC master.dbo.sp_addlinkedserver @server = N'LinkedServerName'
                             , @srvproduct=N'###.###.#.###:####/SRV1'
                             , @provider=N'OraOLEDB.Oracle'
                             , @datasrc=N'###.###.#.###:####/SRV1'

EXEC master.dbo.sp_addlinkedsrvlogin @rmtsrvname=N'LinkedServerName'
                                ,@useself=N'False'
                                ,@locallogin=NULL
                                ,@rmtuser=N'OracleUserHere'
                                ,@rmtpassword='passwordhere'
GO


Then go back in and change your options via the GUI (RPC, RPC Out, etc.)