When you installed windows XP it installed itself to one of the hard drives and set up a boot record on the first drive, pointing to it own start up sequence. This is normal.
Then you installed Fedora. It also needs a way to start up. There are at least two ways to choose between these:
- Let it boot into the start up menu of Fedora (probably GRUB) where you can select Fedora or XP.
- Let it boot into the start up menu of XP (bootmng), where you can select XP and probably also Fedora.
I think you installed the Fedora manager and it worked. Then you booted into XP and it detected changes to the start up parts. Those were benign and without changing them everything would have worked. (Read: if you pressed 'no' all would be fine).
However some older style virusses also modify these things, which is the reason your anti virus cam with a warning. When you pressed 'yes' you wiped the changes which Fedora made.
You now have two choices:
- Change the XP bootloader so it also recognises XP.
- Boot Fedora again (from a CD or pen drive) and reinstall its bootloader.
To change the XP bootloaded, look for the file
boot.ini on the C: drive and edit it so it resembles the contents below.
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Windows XP" /noexecute=optin /fastdetect
Note that you will need to locate and copy the relevant fedora.bin part to your C drive. Since you already have the Fedora installation media that is just a question of copying the right files.
The other alternative it to reboot the Fedora installation, reinstall or reconfigure GRUB and press
no when you boot back into windows. This might be as single as booting Fedora and running
grub2-install /dev/sda again (which will reinstall itself into the MBR).