Problem with Micro SD card breakout
Did you try:


Reading the SD card in your computer ... if  you can read (or write) files, that means the SD card is intact
Use a SD card that worked before or similar. Some bigger SD cards (like SDHC, SDXC have less good compatibility). Preferably use a 2 GB or smaller card (unless you have used bigger cards successfully and of the same or smaller type, e.g. SD, SDHC, SDXC). 
Try different formattings, like FAT, FAT16, FAT32. I think FAT is the mostly recognized formatting.
Check connections/wires to/from SD breakout, maybe during your leave accidentally you (or someone else) or due to pressure/tension, a contact/wire got loose.
Check another SD card in the SD breakout where the SD card you know is good. If this also does not work, it must be the breakout (or Arduino).
Replace every piece of hardware (including wires) one by one and recheck if it works (after you are sure the SD card itself is ok).