So to summarize, if you go into Disk Management, you should see two partitions, the first one small (350 MB) possibly saying System Reserved and no drive letter, also saying active: the other being the remainder of your disk that contains the operating system, and probably with labels of Page File and Primary Partition, probably labeled C. Right click on this larger partition, select "Mark Partition as Active", it will give an error message saying you can only have one active partition, say OK. Now resume the upgrade. Be sure you have the ability to boot off of an installation disk or USB (you should test this first, Google it if you don't know how). As always, caution says you should back up your data before trying this, as it can make your you system inoperable if you cannot repair it.
