I have a compaq cq70 which will only boot into safe mode also, the screen is upside down. I have tried everything I know, but I am now absolutely lost as to what the problem could be.

Any assistance would be gratefully appreciated.

Since you mention 'safe mode' I assume that you are running a Windows operating system. To resolve the upside down screen try using Ctrl/Alt/up arrow.
Are you able to get the boot menu to display by pressing F8 during startup (and before the Windows logo appears)?
It could be a faulty device driver that may be causing the problem. Have you added any new devices?
If you have a Windows installation DVD available, you could try doing a Repair by booting from it.

Adding to whtat mlesniak said above, with windows you have the default back up and restore program, if you made an backups you may luck out and be able to restore to a previous version. I just had this problem last Wednesday, BSOD on boot but was fine to boot to safe mode, I restored a backup and it fixed the problem.