If you can edit the registry then change the Value of the Start
sub-key under the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\sptd
key to 4
However, considering that you can't even go into Safe Mode - which does not load the SPTD driver at all, I think there might be deeper issues here.
You should back up your data now.
One way you can do this is by using Ubuntu. This is completely free, and has the advantage that it can be run off a USB stick or a CD - saving you having to install it on your hard drive.
You can get it from here: Download | Ubuntu
Step #2 on that page shows you how to create the USB/CD.
Then once you boot into it (choose the option where it just runs off the USB/CD) you can use it to copy your files from the Windows Partition to an external hard drive (Note:
Do not copy anything to the Ubuntu Filesystem as it will not be saved on shut-down)