I readthat I must downgrade to 1.5 again then go to 3.4 OE but don't know how to downgrade to 1.5 from 3.10 OE-A. Please help... Thanks.

Use recovery mode. Make sure you have the files neccessary then scroll and click the option that says runprogram at GAME/RECOVERY/EBOOT.PBP (< it may not say this exactly but it's pretty close you can't miss it it's one of the first things located in recovery.) Here's the recovery files if you don't have them already. I have already put the 1.5 update in there it's named UPDATE as it should be.

http://www.megaupload.com/?d=25M24IIX

Recovery files... where?

Sorry I editied it the link is there now I made an oopsie and clicked post before I was done. Here's how to use.

1: Extract recovery

2: Place Recovery folder in the GAME folder (NOT GAME150)

3: Hardset PSP and access recovery mode

4: Move down and click the option as I said in my post

5: It'll run and ask you to press X to flash yer PSP click X (DO NOT HARDSET OR UNPLUG AVC CABLE UNTIL PSP SAYS OTHERWISE!!!)

6: Welcome back to 1.5 feel free to run whatever you want now.

Thank you very much!... What is this all about ..

"2.71->2.80->1.5->3.03 OE-C->3.10 OE-A->3.10 OE-A'->SEMI-BRICK->1.5(recovery)->3.10 OE-A->3.10 OE-A'->3.40 OE-A (caused major unknown error now PSP won't function on OE FWs and I can't update past 3.11 due to the fact that I have a patched TA-082 mobo)->1.5(recovery)->3.00->3.03."

??? I believe mine is a TA-082.

Well I was on 3.10 OE-A' just like you I restored to 1.5 and went up to 3.40 OE-A and my ISOs wouldn't load so I restored back to 1.5 and ran the 3.10 OE-A update and when I go that bluescrren that says to push O I did nothing happend so I hardset my PSP and now anytime I try to run CFW my PSP attempts to make itself Jap region. I would recemmend not updating and saying on 3.10 OE or going back to 1.5 than to 3.03 OE-C there's not even a game that requires FW higher than 3.0 yet so there's really no need to update. The coolest thing about 3.40 OE-A is that the autoboot feature returned. So my advice to you would be to stay at 3.10 OE or go to 3.03 OE-C. But there is no full blown proof behind this it could have just been a freak accident.

Surely you can just put the 3.40 OE flasher (with the DATA.DXAR file) in "ms:\PSP\GAME150\".
Then you can go straight from 3.10 OE-A to 3.40 OE-A.

Well his read me said to go back to 1.5. I think he's following it to be better safe than sorry would ya say?

I had semi-bricked again that's why I went back to 1.5. I really do think this is something common amongst patched TA-082s because stories very simillar to mine are poping up everywhere. My PSP is with Sony (it was running 3.03 OFW when I sent it in so as not to have my warranty voided) They're gonna send me back a stock PSP so I'll be able to downgrade and run CFW again h00rayZorZ!

I think he said that he read that he had to go back (not from a Readme).

I agree that it is always better to be safe than sorry.
However, I think that going directly from 3.10 OE-A to 3.40 OE-A is actually safer, because you always have the recovery menu.
But it doesn't really make that much difference either way.

Thanks for all your help!