Although this question is really old I would like to answer it as I had the same problem a few days ago. This first answer from ikkenom is not really good, it is to general.
If your Aopen XCube UX45G forgets BIOS settings like time, boot order or other options it is very likely that the battery needs to be replaced. To replace the CMOS battery of the XCube UX45G you need a new CR2032 battery. The battery socket is a bit hidden. It can be found next to the IDE ports. See this image: http://www.informationsarchiv.net/uploads/image/8182/xccubeez65-25.JPG
. First turn of the power chord, remove the battery as ikkenom described and insert the new battery. The positive pole (+) has to be positioned in the way that this pole can "see" the RAM slots. Turn back power chord, start the computer und reset BIOS settings.