Black screen appears after going through BIOS.

I am having a strange problem.After going through the BIOS, my computer shows a blank screen for 30 seconds before the Windows loading screen appears. First I thought that it is a problem with graphics card and so I replaced the graphics card last day but the problem is still as it was. I have searched a lot on Google but found no luck yet. Can anyone here please take me out from this problem?
This is Windows XP SP3 and everything is updated with this.
