Hi Angelo!
Most of the time that I have ever had problems with passwords it turned out to actually be problems with my keyboard. So now, from time to time, with the power off I invert the keyboard and while tilting it in several directions operate the keys (sort of tapping from underneath) and then spray - from underneath from several angles - Electronics compressed gas duster air spray (e.g. Dust-Off). The idea is to get the gunk that normally gets into the keyboard and under the keys out of there so that they can work consistently. You really do need that for passwords.
But looking at the second group of problems that cropped up as you tried to boot into single user mode, well, my attention turns next to your disk (but memory may be easier to check). Do a memory check if you can (often a boot menu option). Then, assuming your disk is the normal spinning disk type (not an SSD) use fsck and/or badblocks to test the health of the disk. The old spinning disks tend to fail in a specific area (at first at least) and so the usual disk check facilities off load a section of the disk and then write to and read back on that section to test. I lost my Windows disk on this box I am using a couple of months ago. A section of the disk was faulty - major errors when it tried to test that section. The rest of the disk seemed to do fine. At any rate I would check the disk. Use only non-destructive testing of course. It takes a long time with today's bigger disks. If I recall it took about eight hours to process my modest 160GB disk.
Also, it may well prove worth your time to use Clonezilla to take an image "snapshot" of the disk at this time. When my disk did fail a lot of time was saved by having an image on hand to use on the new disk (actually I had two identical disks as part of the original box build - identical disks are very nice with using Clonezilla). If you end up replacing the disk basically you will need a same or bit larger disk for Clonezilla to be happy although I hear that there are options.
Working with Fedora (I am no expert with Fedora) my tendency for doing a re-install is to use live disk Parted to erase the Fedora partitions (and swap) and then install from a Fedora live disk. The installer will see the free space and gladly use it. Part of the install process does a fresh install of Grub 2. So Grub 2 will see your untouched XP partition and make a boot menu path to it.