First, if you have an A70HB, I assume a V1 because I think the v2 was model A70BHT, do you know if you have the 2 or 8 GB model? Either way, the fix will be the same. If you have the 2 GB model, I wouldn't recommend flashing the firmware with anything but the manufacturers firmware. If it is the 8 GB model, you have a little more freedom, but you definitely should not try running Gingerbread on it. I personally wouldn't recommend running 2.X on it only because it was geared for machines that accept multi-touch input and accelerometers, neither of which your tablet is capable of. However, you don't have to stick with the stock firmware either.
But I digress, you need help fixing your tablet. No guarantees this will work, but this is a process than can help unbrick many a unit. Yours isn't quite bricked, but it might as well be.
PLEASE READ THIS IN IT'S ENTIRETY BEFORE PERFORMING ANY ACTIONS, INCLUDING THE NOTE ABOUT THE SD CARD POSSIBLY BECOMING READ-ONLY. I just don't want to be blamed for some quirky behavior after the flash.
The first thing you need is a program called RKAndroid Device Manager. It is for machines based on the Rockchip RK2808. You can find it here from Google.
RKAndroid_ENG.zip - apad-irobot - Rockchip RK2808 Updater Tool English (RKAndroidDMv1.2) - Apad iRobot Rockchip RK2808 Android Tablet - Google Project Hosting
Go to Archos' website and download a copy of the factory firmware, or go to the ArchosFans forum and find an OS image there you would like to try. I run the Knight Dominion firmware on mine because it is faster and more stable than the factory firmware while being based on it, plus it adds the Android Market to the machine on top of the AppLib from Archos.
Forum.ArchosFans.com - View forum - Archos 7 and 8 Home Tablets
WARNING: THIS IS A DESTRUCTIVE PROCESS AND ALL DATA WILL BE WIPED FROM YOUR ARCHOS!
With the update.img file unzipped to a folder somewhere on your PC, turn off your Archos and push the power switch to the right to lock the screen. Now use a paperclip or something to press the reset switch on the back for several seconds. Now tether your Archos to your PC and it should detect it as a new device even though it didn't work before. (Do not power it on! Leave it off and locked.) There are drivers for it located in the folder where RKAndroid is extracted, so navigate there if you are prompted for drivers. Note, I have heard it may not work with 64-bit operating systems.
The interface on RKAndroid should show that the device was detected. Press the ... button next to New Firmware Information and select the update.img file for the new firmware you selected. Click Restore and it should wipe the old firmware off the hidden partition and reinstall with the new one you selected. Once it says it was successful, safely disconnect the Archos from the computer and power it on. It will complete the firmware installation and you should be back in business. You may have to tether it to your computer and format the internal flash memory on your Archos before it is useable again. Just use the standard Windows defaults for formatting when you go to do it. After formatting, the firmware will automatically recreate the music, video, and other folders.
Of note, after flashing the firmware on my Archos I can no longer write to the SD card. It can read it just fine, so I just tether it to my PC and use the SD card to store .APK files for apps that I want to be able to run, videos, and MP3 files. The Knight Dominion firmware frees up around 230 MB for system storage, so you can install quite a few apps in that space.
Hope this helps!