Can I get 100% protection from virus by using Deep Freeze?

There are oodles of non-local-harddisk places that malware could stay (although in practice, such is rare in viruses). A few, off the top of my head, the system BIOS (although rare, there is malware which does this), or the firmware of bootable PCI cards.

If a virus can get on to your system, though, preventing it from persisting won't help - it may simply re-infect you after your reboot. Some 'stealthy' malware will stay entirely memory-resident, and will not write to disk, in order to evade detection.

Maybe you need to examine what you're trying to prevent - instead of 'A virus', maybe the answer is 'damage to my documents' or 'exfiltration of my documents'... or even simply 'theft of my banking credentials'. This might help you focus on what threats you should be preventing.

No, the "virus" can still run and read your (sensitive) files, just like if you are not using Deep Freeze. Only after you restart your computer, will the malware (virus) be gone and you will be presented with the clean state (whatever state was frozen).

In addition to the answer Matrix gave, there is the possibility of a virus modifying firmware allowing it to survive past complete drive content resets.