Can I access my trunk from the back seat, & how?

Use the key to unlock the back seat, release the back seat and fold it down, climb inside the trunk, and pull the trunk release lever.

The rear seat backing will have to be removed to access the paneling and lock assembly to open if the lever/remote is non functioning. Sometimes banging with your fist just above the lock while someone operates the release lever will open the trunk

If release lever is not functional, use key. If key will not turn in cylinder, spray WD-40 into cylinder and use sawing motion to get key inserted and continue sawing motion to free up lock wafers internal to cylinder so it will turn with key. If this process is not effective, you will need to remove rear seat to access paneling to trunk lock and open accordinly

Wrong keys or wrong car?. lOL
the cable release won't work if the trunk kew was in lock horizontal position. It needs to be vertical when key is removed. More penetrating fluid and try to force key rocking back and forth in and out. Use lots of wd40 or penetrating fluids and repeat. This will work. Also make sure you are using a master key only. Black top.

It is really unclear what the problem is please rewrite.

Valet Key ? 0nly does the drivers door & ignition

does the key turn the trunk lock?if not theres one issue right there.the other may be that the valet lever on trunk latch assy. may have inadvertantly been engaged if deck lid was slammed closed.the release solenoid will make noise when activated by fob or lever in car but because of valet being engaged cannot release latch.does key unlock glovebox?if not this may also be a valet key cut.contact nissan dealer to cut regular key.ive seen the slamming the deck lid scenario a million times as the valet lever takes hardly any effort to engage.good luck and let me know how you make out.

Check for a drivers side interior cabin trunk release lever or button if not remove back seat to get access to the trunk..
possibly the rear seat might even fold down.

the release cords are located inside the trunk, try popping out the back seat, you will see the gold, 14mm(?) bolts holding the seats in, maybe you can get in by taking the back of the seat out, good luck

I have a corolla 2003 and I had the same problem. I turned the key to the left and the lock turned left, engaging the valet parking mechanism. I could not turn the key to the right and could not get access to the trunk because the lever next to the driver seat was disengaged.
The way I solved this problem is as follow:on the back driver seat I pulled the back seat forward to leave an opening and snick my arm in the trunck. Then I grabbed the cable used to latch the seat and I pulled forward, i.e. toward the front of the car. The cable is connectred to the trunck so that it can be disconnected easily if pulled towards the front. If you pull towards the back it will remain attached to the trunck. So grab the cable an pull towards the front, and it will release itself. Since the cable is flexible, you can pull it out of the trunk from the same the opening you put your arm, and then disenagage the driver back seat. Fold forward the back seat and get into the trunk and use the lever in the latch of the trunck to open it. The turnk will open.

If the lock does not turn, you need to disconnect the lock from the mechanism, so that the driver seat lever can start working again. To do this, and with the trunk open, remove the cover holded by nine plastic pins. Do not break the pins. After removing the cover, you will see the lock holded by two nuts. Remove the nuts with a rachet. The lock will be loose, and disconnect the lever that connects the lock to the latch. At this point the driver seat lever will start working again. Close the trunk and verify that the driver seat lever opens the trunk. Now you can open and close the trunk , and have time to call the dealer for a new lock.
Good luck.