I've included a sample report below that lists your Windows computers, their uptime and their last boot. Instructions for adding this report to your Lansweeper installation can be found 
here.
Select Top 1000000 tsysAssetTypes.AssetTypeIcon10 As icon,
  tblAssets.AssetID,
  tblAssets.AssetName,
  tblAssets.Domain,
  tsysAssetTypes.AssetTypename As AssetType,
  tblAssets.Username,
  tblAssets.Userdomain,
  tblAssets.IPAddress,
  tblAssetCustom.Manufacturer,
  tblAssetCustom.Model,
  tblAssetCustom.Serialnumber,
  tblAssets.Firstseen,
  tblAssets.Lastseen,
  tblAssets.Lasttried,
  Convert(nvarchar(10),Ceiling(Floor(Convert(integer,tblAssets.Uptime) / 3600 /
  24))) + ' days ' +
  Convert(nvarchar(10),Ceiling(Floor(Convert(integer,tblAssets.Uptime) / 3600 %
  24))) + ' hours ' +
  Convert(nvarchar(10),Ceiling(Floor(Convert(integer,tblAssets.Uptime) % 3600 /
  60))) + ' minutes' As Uptime,
  DateAdd(second, -tblAssets.Uptime, tblAssets.Lastseen) As LastBoot
From tblAssets
  Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
  Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
Where tsysAssetTypes.AssetTypename = 'windows' And tblAssetCustom.State = 1 And
  tblAssets.Uptime Is Not Null
Order By tblAssets.Uptime Desc