[Transformer TF300T Q&A, Help & Troubleshooting] mikedenney:
Resolved it this Way

FOR EVERYBODY OVERLY [SOMETIMES SICKENINGLY] FAMILIAR WITH WINDOWS MANUAL DRIVER INSTALLS, HERE'S WHERE THOSE MTD DRIVERS ARE PUT BY THE ASUS SYNC FOR WINDOWS XP DOWNLOAD:

C:\Program Files\ASUS\ASUS Android USB Drivers\MTP

FOR EVERYBODY ELSE, READ ON:

Hey, had the same issue here, thinking it was the fact that ASUS is showing nothing past XP under their Windows downloads, so maybe a compatibility issue with their Sync setup (primarily, not copying the MTD drivers to the correct place during setup).

Having had MUCH WORSE issues with my fave little ol' Sansa Express MP3 player years ago when its battery died completely, I cracked my knuckles, sighed, and dug in for a long haul.

Luckily, I tried this first, since dealing with Windows version compatibility is much more common, so more familiar/easier.

(Of course, I was doing something different, but I'll be doing what you're doing, soon enough).

Download ASUS sync for your tabbie here:

https://www.asus.com/Tablets_Mobile/ASUS_Transformer_Pad_TF300T/#support_Download_17

Of course, it puts everything where it should, except the very important MTD files--but obviously ASUS included them--for me (32-bit Win7), they were HERE:

C:\Program Files\ASUS\ASUS Android USB Drivers\MTP

Plug your tablet to your PC via it's USB cable, wait for the Windows driver search to appear, then tell Windows to 'skip obtaining driver software from windows update'. Let it fail (that's where some of the best stuff begins!)

Go to Control Panel, Device Manager...open it.

As with some of the worst driver issues I've seen, I didn't see anything other than a single driver there--'ASUS Transformer Pad TF300T'' (see pic)--so I clicked 'Action' up top, then 'Add Legacy Hardware' (single-click something in the lower driver listings to enable this option), then 'Next', then 'Install the hardware that I manually select from a list', then 'Show All Devices'.

You don't have to wait for this list to populate--just click 'Have Disk', then 'Browse', then find the proper ASUS MTD driver at the location I described in this line above-->>>C:\Program Files\ASUS\ASUS Android USB Drivers\MTP

These will be annoying click-out submenus, but be patient--you're almost done.

Click through the rest, and you're done...NEARLY.

As is typical with this manual driver stuff (esp. storage drivers like this), I had to restart my PC to finish this driver install (and 'yes', I really did try and cheat Windows out of another 10 minutes of MY LIFE by running the ASUS Sync program on my PC, but it didn't work until rebooting).

Spoiler alert! (Upon reboot, it worked)

[ahem]

Upon reboot, it worked. I ran ASUS Sync, and [finally!!!] am seeing it recognized my tablet as what it is, and life began again after my millionth+6 Windows driver issue. (PLEASE remind me to personally 'thank' Bill G. wherever I see him after death).

EPILOGUE:

Why ASUS failed to update its driver update page after Windows XP, I'll never know, this being a little harder than the ole 'Compatibility Mode' install route...but this worked for me, and despite this little stutter-step, I'll be reaping whatever benefits ASUS sync gives me, but honestly, it wasn't even what I needed to back up my Home Page settings on my TF300T in order to factory reset the thing, because, like some here, mine is performing MUCH slower than it should, even in Performance Mode (but, hey, I got mine from a local pawn shop, so--that's expected, y'know).

ENJOY! Hope this helps, most of the time I feel I've nothing to contribute here...XDA is WAY over my wittle head!

What's really odd is that, even after doing all this, my Device Manager driver listing for the tablet still looks like the attachment I posted here, yet the thing appears to be working fine. Double-clicking on the 'kicked-out' drivers shows 'Device Failed to Start'...this is probably because Windows isn't actually using the ADB and MTD drivers until immediately upon running the ASUS Sync application, though.