C#, Can I check on a lock without trying to acquire it?

I have a lock in my c# web app that prevents users from running the update script once it has started.

I was thinking I would put a notification in my master page to let the user know that the data isn't all there yet.

Currently I do my locking like so.

protected void butRefreshData_Click(object sender, EventArgs e)
{
    Thread t = new Thread(new ParameterizedThreadStart(UpdateDatabase));
    t.Start(this);
    //sleep for a bit to ensure that javascript has a chance to get rendered
    Thread.Sleep(100);
}


public static void UpdateDatabase(object con)
{
    if (Monitor.TryEnter(myLock))
    {
        Updater.RepopulateDatabase();
        Monitor.Exit(myLock);
    }
    else
    {
        Common.RegisterStartupScript(con, AlreadyLockedJavaScript);
    }
}

And I do not want to do

if(Monitor.TryEnter(myLock))
    Monitor.Exit(myLock);
else
    //show processing labal

As I imagine there is a slight possibility that it might display the notification when it isn't actually running.

Is there an alternative I can use?

Edit:
Hi Everyone, thanks a lot for your suggestions! Unfortunately I couldn't quite get them to work... However I combined the ideas on 2 answers and came up with my own solution. It seems to be working so far but I have to wait for the process to complete...

Ok this seems to be working, I broke out the Repopule Method into it's own class.

public static class DataPopulation
{
    public static bool IsUpdating = false;
    private static string myLock = "My Lock";
    private static string LockMessage = @"Sorry, the data repopulation process is already running and cannot be stopped. Please try again later. If the graphs are not slowly filling with data please contact your IT support specialist.";
    private static string LockJavaScript = @"alert('" + LockMessage + @"');";
    public static void Repopulate(object con)
    {