Sounds like you might have just accidentally knocked the sata and/or power cable from your OS hard drive...
Just power down completely, and look at the connections on the back of your hard drive(s) for a connection that popped out or is loose...
*also look at where the SATA cables attach to your MB connections for the same thing.
Its easy to check and see if thats the problem...
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http://www.asus.com/Desktops/Essentio_CG5290/It appears that you unit has a OEM power supply rated a 500w "peak" and thats not good even when the system was new 5yrs ago...
I cannot find -any- information on it at all, and thats not good either
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If you dont find any loose connections to the OS drive, the next step would be to boot into BIOS and see if all you need to do is re-point the boot sequence to the correct hard drive as your BIOS may have reset with the addition of the new card.
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Your Download page
http://www.asus.com/Desktops/Essentio_CG5290/HelpDesk_Download/It appears the last BIOS update for your motherboard was in 2012
post edited by maniacvvv - 2014/04/19 02:10:42