div containing background image moves upward and downward in asp

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ASP.NET

I have a div containing background image in asp content page connected with master page
my problem is when we moves scrollbar of browser downward using mouse or by using down arrow key of keyboard to see content of footer or something like that the asp page is moved upward and vice versa when scroll bar of browser is moved upward the asp page is moved down.

i have used style="position:absolute" for div and also tried using style="position:fixed" but that doesn't work with master page content and have used
jqueries from stack overflow but still it didn't work. also tried

<div style="overflow:auto; height:100px; width:auto " >
</div>

along with this i am running asp timer on my webpage with its tick event

<asp:Timer ID="tm" runat="server" Enabled="true" Interval="1000"    OnDisposed="Timer_Disposed" OnTick="Timer_Tick" ></asp:Timer>

with a tick interval of 1 sec if this is beacuase of timer tick event then pls

pls help me out with this .