For your first attachment (Excel), I have few suggestions. You have to avoid spaces in between the column names, for all the excel sheets which will be used for SD export. Better to mention the column names in upper case. Specific to this case, you must have Location 'OFFICE' and Category 'Dell GX 520' already defined/created in OVSD, because these are reference items to a CI record.
For import mapping, The import mapping name should match the name of the application defined in the export settings. You should map each attributed which has been exported from excel to XML, to a predefined attribute of the CI. Mark at leasr one attribute (preferably search code) as Unique.
To troubleshoot your specific problem, please attach the exported XML file and the import log file..