Your nokia n73 keep displayed "memory full please delete some data"
Currently you do not have any text/photo etc with a large size stored.
Probably your cellphone infected by virus, to repair n73 memory full
1. Put power off, remove your memory card from slot
2. If the problem solved, format your memory card from PC, and put it back to cellphone and reformat memory card from cellphone.
3. If the problem not solved, set your n73 to default factory setting by pressing *#7370#
Standard code is 12345
4. If the problem not solved, upgrade firmware / upgrade software
upgrade/reflash firmware need repair box (like Ufs3, Jaf, MT Box, etc)
note : remember to back up your contact or other data first.