Safe mode = Windows. Exact version is unknown.
You may have a missing file or two on your boot drive.
To get sure, get a Linux live CD and boot with it. Use it to take a look at your boot drive.
You should see the following files (windows XP):
AUTOEXEC.BAT (size = 0)
CONFIG.SYS (size = 0)
IO.SYS (size = 0)
MSDOS.SYS (size = 0)
SOME of those may change if you have another version of Windows than XP.
The absance of ANY of those files may prevent your system from booting.
The files NTDETECT.COM and ntldr allow you to boot from a NTFS formated drive.
Check if any of those is in the recicle bin. If so, try to move them bact to their proper location.
If you can't recover them, you'll need to reinstall Windows.
Use the Linux live CD to do a backup of your datas BEFORE you start to reinstall.