Everything you need can be found on this site and/or the FTP (
ftp://up.ppcgeeks.com/titan). I'm a little unclear on the steps you've taken so far. Can you tell us step by step everything you did to initially install the new ROM. Don't leave out any details.
Here are a few things you can try though (mostly reiteration of what hotbyz said). Trying from an XP computer might help. I always flash mine from Vista, but there is usually less troubleshooting to be done with XP. Start from scratch.
The old bootloader/relocker is here:
ftp://up.ppcgeeks.com/Titan/Users/Im...n_Relocker.exe
I couldn't get 2.17 to reload when I tried, but if you want to give it a shot the .nbh is here:
ftp://up.ppcgeeks.com/Titan/Users/Im...RUU_signed.rar
You'll just need to put that nbh file in the RUU folder and run RomUpdateUtility.exe. Here is a link to the RUU:
ftp://up.ppcgeeks.com/Titan/Users/Im...N/roms/RUU.rar
If that doesn't work you can try flashing 2.17 from the SD card (again didn't work for me, but it was my first attempt at flashing from SD). I've heard the card needs to be formatted in FAT32, so do that first. Then rename the .nbh from above to TITAIMG.nbh and place it on the root of your SD card. Put the card in your phone, and go into bootloader mode (Camera+Power+Reset simultaneously). Should start flashing the image from the SD, at least that is my understanding.
If you can't load 2.17 at all, and you're still stuck in the bootloader, just try flashing to 3.35 from the official update exe. Maybe try a fresh download of that too. There are mirrors all over the place, but I know the one on the FTP worked for me:
ftp://up.ppcgeeks.com/Titan/RUU/RUU_...CS_AM_Ship.exe
If that still doesn't work you can try extracting the nbh from that exe and flashing from SD again using the method described above.
If that doesn't work try loading Olipro's 2.40 bootloader from here:
ftp://up.ppcgeeks.com/Titan/Users/Im...rd-SPL-MFG.exe
Then try reloading 3.35 with both methods above. I'm sure you've already tried a lot of this, but I was just trying to give you some ideas of steps you can take, and a consolidated source of links so you don't have to hunt around. Hope that helps
Let us know if you get it sorted out.