No approach is 100% foolproof. That being said, the best
(safest) approach is to:
1. Copy all your data as a safeguard. You can either phyically
remove the hard drive and place it either in an external
enclosure or in another PC as a slave *OR* boot off an
emergency CD like Knoppix, Ubuntu, UBCD4Win, or Bart PE and
copy the data to an external hard drive. Once this is done,
data can be copied to another location. (Feel free to ask if
you need guidance.)
2. After pressing F8, attempt to start your PC by using the
Last Known Good Configuration:
http://support.microsoft.com/kb/307852
(Who knows? You might luck out with that!)
3. If the above doesn't work, perform what is often called a
manual System Restore. Instructions are here:
http://support.microsoft.com/kb/307545
If you have an XP installation CD, you may the Recovery Console
found there. (Or perhaps it is a choice in your F8 menu.) If
you don't have an XP installation CD, you may burn your own
bootable Recovery Console CD, using the information here:
http://tips.vlaurie.com/2006/05/recovery-console-for-those-witho
ut-an-xp-disk/
If you need a program that can create a CD from an .iso, I
recommend ImgBurn:
http://www.imgburn.com/
Another option is a Repair Install, but these can be tricky
with regard to Service Pack levels not matching and the version
of IE installed. If the above doesn't work, post back and we
can give you better guidance with regard to performing a Repair
Install (its advantage is all your programs and data would
remain intact -- *if* done without issues...).
As I said, the above is not 100% foolproof, and the possibility
exists that you will need to perform a Clean Install. :-( Its
disadvantage is that all your data and programs would be
erased. That is why it is important to back up all your data!
In the future, if you want to avoid this situation (the
possibility of losing all your installed applications), it is
best to regularly image or clone your hard drive. If you would
eventually like guidance for that, please start a new thread.
Good luck.