Something like this?
SELECT
AssetTypename, COUNT(tblAssets.AssetID) as Total
FROM
tblAssets
LEFT JOIN tblAssetCustom ON tblAssetCustom.AssetID = tblAssets.AssetID
LEFT JOIN tsysAssetTypes ON tsysAssetTypes.AssetType = tblAssets.Assettype
WHERE tblAssetCustom.State = 1
GROUP BY AssetTypename
Order By Total Desc
The results should look like this
AssetTypename Total
Monitor 1234
Windows 4567
Printer 890
Webserver 123
IOS 45
VOIP phone 6
Linux 4