Plus, after she defragmented it, my free space went down from 102 GB to 76 GB. Is that also a problem?
it shouldn't have taken 12 hours. 30-45 minutes depending on the size of the drive and amount of fragmentation. check to see if it has bad sectors. run a diagnostic on the HDD using one of various diagnostic tools available online.
making a back-up is always beneficial. u might have to change ur HDD..but don't rush into it. most branded pc's give u a diagnostic software with their system and in-case of an assembled pc..well..there r plenty of really good software's available on the net.
I'll probably look more into this.