I think it's an OS related issue. Everything should work fine after the OS re-instalation.
Before you re-install the OS.
Update the BIOS to latest (if not done already).
Latest bios for this board can be downloaded from the following link: http://downloadcenter.intel.com/Detail_Desc.aspx?agr=Y&Inst=Yes&ProductID=2932&DwnldID=17617&strOSs=38&OSFullName=OS%20Independent&lang=eng
- Do the bios update either by the recovery method or the iflash method: http://downloadmirror.intel.com/17617/eng/BIOS%20Update%20Readme.pdf
Note: For recovery method you can also use a usb pen drive (empty and non bootable).
- After the bios update is done, then proceed with the OS installation.
- Remember if you are using windows xp installation, it has to be with at least with service pack 2.
- After OS installation, install the motherboard drivers.
Note: You can download the latest drivers: http://downloadcenter.intel.com/Product_Filter.aspx?ProductID=2932
- Remember to always install the Chipset (INF) drivers first, then audio drivers then the remaining other drivers.
- If there is any front panel usb and audio, you may have to disconnect then before os installation and connect them at a later stage when the OS is already installed and working properly.
- You may also need to check that the power supply you are using satisfies the power requirements of the board: http://support.intel.com/support/motherboards/desktop/dp45sg/sb/CS-029162.htm
If even after doing all the above, the issue remains, then you may need to remove the motherboard from the casing and test it out of chassis.This problem can also be caused by short circuit. Also you may try with different keyboard and mouse and in different USB ports.
Hope this will be helpful for you.
buddy do also chk out some other threads regarding with this board DP45SG lot of problem is going on with this bloody board specially USB Ports powers runs out, Board is not stable with high voltage things like tht wht u have suggest below i have done everything but at last i had to send my board in warranty and up till now i have been know there 5 ppl here they have change the board to other brand ASUS and there is no official help or even not a single word from intel in this senario which is really really frustating we love intel i love intel and i dont wana change my board so easily but as i am seeing here Intel is not supporting us this time very well and tht pretty much bad any how u do chk and let me know wht u think of the Issues i mentioned above and wht will be the rectification for it pls do reply