My old Sandisk 8Gb suddenly cannot rewrite and reformatted, and my PC cannot detect new 16gB Ultra.

I have 8GB sandisk class 4 and have used it a year ago. I have no problem with reformatting it and to read and write in my Dell vostro and Acer travelmate. Even my cheap panasonic digital camera and my olympus pen can read and write with no issue.  Until three weeks ago I got a new 16GB ultra and has used it with my olympus pen and has no problem taking photos.  I swapped 16Gb and 8GB to pana & olympus camera and they have no issues.

Until one day I insert the 16Gb in my PCs, all of them cannot recognize the sdcard. I have to transfer all photos inside 16GB to PCs via the olympus transfer cable. The cameras can still taking pictures and reformatted the 16GB, except that my PCs cannot detect it.

At same time I found my pana camera cannot store photos after snapping hundreds in 8GB taking about 3.5GB of it. However my PC still can read it, copy photos to PC but the problem is it cannot further rewrite or reformatted in cameras or PC. It took hours to delete  the data inside 8GB but the data keep residing in it.

This is frustrating and I am about to ask refund and purchase Kingston or Transcend which I have using them since 5 years ago without having problems.