Seems that the install is not for USB. failed to mount block device....
Do you have secure boot or UEFI ? This can cause all types of issues when using a recovery disc. Go into BIOS when you boot up computer. Its usually something like F10, F8 F5 F12 etc.
Make sure in BIOS secure boot and/or UEFI is disabled. (if you have it on your BIOS not all do, also look to see Legacy Boot is enabled) Here is some info from Kaspersky on Booting From UEFI mode here. Over all if you can burn the ISO to a DVD, and then boot from CD, it causes a lot less issues, and resolves itself
Make sure you disable Secure Boot/UEFI first and reboot, then enable Legacy Boot and reboot. (i know you really cant reboot but you get what I mean, save and exit and turn off and on.)
Was this computer down graded from WIndows 8 to windows 7?
What USB installer are you using?
Can you run it in Text mode? Do you know how?
When you downloaded the .ISO file to the USB did you use the Kaspersky tool? Remember first to format that USB dive in FAT 16 or 32, then use the Kaspersky tool. See more info on it here.
Lastly, when you are using this from a USB did you read page 13 on of the PDF that is on the site? It lists specific items that you need to edit and change to make this work right? Here is the link to the PDF here.
Overall, I would burn it to a DVD, you can use windows for that. Its easer and has always worked for me. Also if you dont have DVDs to use and need to use the USB, read on how to boot from text mode in the PDF. I would suspect the issue is that this tool loads, then performs a action, then grabs more info from the DVD/USB and works somemore. Its a pain but to run alot of items from USB that are made from DVD you have to edit items in them. I use easy USB 123 which you can find here.
Again using a Linux tool in a windows enviroment can be tricky but can be done.
Overall, I guess I should of explained this better, I didnt want you to use this as a virus tool. Meaning when the scan starts stop it. Click X or stop.
Go to the desktop that is there, its a bit tricky but by going into the file path, if you click in the bottom right corner, or right click sometimes works you can get to the file path. Go to C:/ drive, and there are all your files. You can plug in a external USB drive and save all files from your Documents/music/videos/pics and downloads there. This is most of the files that anyone wants on their computer.
Then if you have a windows 7 installiation disc you can do a clean reinstall. (this delets all your files on your computer.) To do this follow this guide here. If you have a install disc from windows skip the USB part and go down to the install screen, if you do not the first part will guide u through making a USB to do this from. Both work, I just used this to reinstall OS Windows 7 on 3 computers yesterday.
And no you do not need Kaspersky to use the rescue disc. If you do not want to do this, I think you might have a virus, and keeping with the rules for my position here I will get you intouch with a malware removal support tech, who are super smart and can work with you on getting you computer running again.
Please let me know either way.