Try this for starters.
Select Top (1000000) tsysOS.Image As icon,
  tblAssets.AssetID,
  tblAssets.AssetName,
  tblAssets.Domain,
  tblAssets.Username,
  tblAssets.Userdomain,
  tblAssets.IPAddress,
  tblAssets.Description,
  tblAssetCustom.Manufacturer,
  tblAssetCustom.Model,
  tblAssetCustom.Location,
  tsysIPLocations.IPLocation,
  tsysOS.OSname As OS,
  tblAssets.SP,
  tblAssets.Firstseen As [Created at],
  tblAssets.Lastseen As [Last successful scan]
From tblAssets
  Inner Join tblComputersystem On tblAssets.AssetID = tblComputersystem.AssetID
  Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
  Inner Join tsysOS On tblAssets.OScode = tsysOS.OScode
  Left Outer Join tsysIPLocations On tsysIPLocations.LocationID =
      tblAssets.LocationID
  Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
Where tblAssets.AssetID Not In (Select tblSoftware.AssetID
    From tblSoftware Inner Join tblSoftwareUni On tblSoftwareUni.SoftID =
          tblSoftware.softID Inner Join tsysantivirus On
          tblSoftwareUni.softwareName Like tsysantivirus.Software) And
  tblAssets.AssetID Not In (Select tblAntivirus.AssetID
    From tblAntivirus) And tblComputersystem.Domainrole <= 1 And
  tblAssetCustom.State = 1
Order By tblAssets.AssetName