vb6 - computer uptime

hello there,
I am having a problem here with this code and the computer uptime.. it works fine if the PC has been on for days but after months I get -21 something weird..
can someone tell me whats the issue? thanks

>>main
Option Explicit
 
Private Sub Timer1_Timer()
    UpLbl.Caption = FormatCount(GetTickCount, DaysHoursMinutesSecondsMilliseconds)
End Sub
 
 
>>module
Public Enum TimeFormatType
    DaysHoursMinutesSecondsMilliseconds = 0
    DaysHoursMinutesSeconds = 1
    DHMSMColonSeparated = 2
    DaysHoursMinutes = 3
End Enum
 
Public Function FormatCount(Count As Long, Optional FormatType As TimeFormatType = 0) As String
    Dim Days As Long, Hours As Long, Minutes As Long, Seconds As Long
    
    Count = Count \ 1000
    Days = Count \ (24& * 3600&)
    If Days > 0 Then Count = Count - (24& * 3600& * Days)
        Hours = Count \ 3600&
    If Hours > 0 Then Count = Count - (3600& * Hours)
    Minutes = Count \ 60
    Seconds = Count Mod 60
 
    Select Case FormatType
        Case 0
            FormatCount = Days & " days, " & Hours & " hours, " & Minutes & " minutes, " & Seconds & " seconds"
        
        Case 1
            FormatCount = Days & ":" & Hours & ":" & Minutes & ":" & Seconds
            
        Case 2
            FormatCount = Days & " days, " & Hours & " hours, " & Minutes & " minutes"
            
    End Select
End Function

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