Error loading operating system

Well this seems a bit strange, my windows xp loads absolutely fine when my both optical drives are connected but as soon as I disconnect them it says "error loading operating system". I have also checked and changed my bios feature boot option and selected my HDD as the first priority but still it seems there's no change. I have 2 optical drives one is SATA and the other is IDE cable. In any of the case if one is disconnected the "error loading operating system" message flashes. I don't know what is wrong. Also when both the optical drives are connected and using my "boot menu" if I select my HDD to boot first it works fine again...what is happening on disconnecting the optical drives??? Please Help!!!
 
Is your hard drive IDE? If so, is the optical drive set to master and the hard drive set to slave? If so, when you disconnect the optical drive, reset the hard drive to master or cable select.
 
Nope my HDD and one of the optical drive is SATA but the other optical drive is IDE...The HDD is connected to 'SATA 1', the SATA optical drive is connected to 'SATA 0' while the other IDE optical drive is connected to 'IDE 0'
 
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