if your operating system is win2k or winXP (since you meantion restore points) click start button> run. type "diskmgmt.msc" into the run box. check to see your second partition on your second physical disk is still there and has a file system on it. make sure is has a letter assigned to it. if not right click on it and select "change drive letters and paths". give it a letter.
if using win9x use fdisk to verify your 2nd partition is still there and has a file system. what i am thinking is that somehow your partition table is corrupt or missing. maybe a viral infection. yes definately try to restore a a previous point. if it does not work this is what you must do:
basically use winxp diskmgmt.msc to delete/ create partition, format, and use it.