It's OK, we're all here to help. OK, so your problem seems to be getting your tablet to actually READ the SD Cards, right? As I understand it, you plug the card in, open the File Manager, and nothing comes up, am I correct?
Working from that assumption, when you insert the SD Card, does anything show up on the notification bar? Any kind of indication that your device has recognized that an SD Card has been inserted (usually a message saying that the system is scanning the card for media)? If not, it might be two things:
1) Your tablet is not compatible with the card size you're using. Especially with older devices, the maximum size of an SD Card can be limited. So make sure that, say, if your card is 64GB, your tablet can support card sizes that big.
2) The format itself. SD Cards, in order to work with most Android tablets, must have a file format of either FAT32 or Ex-FAT (the first limits the file size to 4GB, the latter does not). If your card was formatted on a Windows Machine as NTFS, chances are your tablet will not be able to read anything off it as this is a Microsoft proprietary format and has not been licensed to be included with Android. Also, if your cards come directly from a camera (especially older ones) and was formatted in there, you might also run into a similar problem with proprietary file formats your tablet just can't read.
I know you say you can't access a PC so easily, but it would help to make sure that the cards can be read on a computer. If your camera can read it but your PC can't, you're looking at camera-proprietary format issues. If neither your camera nor PC can read the card, then chances are it is corrupted or damaged.