Undetected USB flash drives

I have two Sandisk Cruzer Blades (8+16GB), and both can't be detected by win7 PC! They are viewable in diskmgmt.msc.
I have 2 older flash drives that do appear, so imo its not the port/pc.

I have files on these, and wish to try and resurrect these without formatting, any ideas of recovery methods/software?

 

I'm recommending Recuva (pronounced recover) by Piriform. I hope this helps.

 

Thanks mdonah, tried that, but I need to be able to see them first!
Might work later, once they are seen.

 

Start here
http://kb.sandisk.com/app/answers/d...r-flash-drive-could-not-be-detected-by-the-pc

 

Thanks plodr...it gets more confusing...they are seen in other PCs, and files presnt and both working, so its to do with current PC and drive letter I believe.
I tried the drive letter re-assigning by Sandisk, but as it doesn't assign a letter to start with, so I can't change it, message appears "operation failed as console not up to date, refresh", and refresh does nothing.....HELP?!

 

You probably have corrupt SanDisk entries in the registry. Let me see if I can find the directions on removal of those. Once those are gone, the problem computer should be able to see and use the drives.

 

I found the directions.
http://kb.sandisk.com/app/answers/detail/a_id/205/kw/Cruzer Blade

 

This issue has arisen again, and I can't seem to fix.
I actually haven't used them for a while.
Again 2 x Sandisk Cruzer blades fail to shoe up is sys tray on work PC (which normally worked well), and although they show up on home PC, don't open to see/drop files.
I have tried the fix below, but hasn't fixed.
Weird another flash drive does work....so its something to do with Sandisk products!