Yes, the backup cmos battery *might* be borderline here. Ubuntu may not tax things as much as Windoze can. But if you can boot into Ubuntu *every time* then I would not suspect CMOS battery as being the problem here.

There are also virus/malwares out there that exhibit these very symptoms.

There are some things to research and try here (Bing search):

http://www.bing.com/search?q=Can%27t+boo...rc=IE-SearchBox

Also, the Kapersky Rescue Disk (free download, then burn to disk, read the directions first) may also be of help here:

http://support.kaspersky.com/viruses/rescuedisk


--Mac