My trunk lock and release is no longer working in my 2005 Toyota Corolla. Although I can turn the key left and right as per owner's manual, trunk will not "pop open". Back seat release is in trunk; removed bottom of rear back seats only to find them bolted to the floor with bolts only accessable through the trunk. Do I bring to a dealer or my mechanic to open the trunk

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.

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.

Re-adjust the cable and lubricate, repair or replace the lock assembly.

Valet Key ? 0nly does the drivers door & ignition

I was able to pull the left side passenger seat forward enough to get my arm behind it into the opening to the trunk. This is difficult to explain so you may need to borrow your friends corolla to see what I am talking about. if your reach back into the trunk and feel upwards you will feel some half dollar sized holes. one of those holes has the release latch cable in it. If you stick your finger up there and pull towards you, the seat will release and you will be able to climb into the trunk to open it via the glow in the dark emergency release handle. Like I said you may want to check out someone elses corolla to get a better idea of what I am talking about.

If you have rear seats that fold down you can access the latch mechanism from the left side rear seat....if you are flexible. pull the corner of the seat forward to allow your arm to slide in behind. about 14-16" in, feeling up inside the trunk you can feel 3 quarter size holes in the sheet metal. The second hole has the cable release arm. stick your finger up there are pull towards you. this will release the seat allowing it to fold down. Crawl into the trunk. there is a glow in the dark release handle on the inside of the trunk lid to open the trunk. Note, these are instructions for an '04 corolla but I think it should work

You should be able to use the trunk release, If this is the type of release that doesn't require the key to be on to use the release button. Most likely you can just pop it open.

have tires check and balanced, check for build up of debris, could be trunk lock was changed out and does not match key, 

Spray silicon lubricant into the keyhole.

Replace the lock cylinder.

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.