Do you have an internal company helpdesk? I would take it to them for review. Some of the things they will look at include:
Windows event log – what errors show up in these logs around the time the computer freezes?
Any new software installed lately?
Could anti-virus been updated with a bad definition file or is it corrupted?
Any malware (ad-ware, spyware) running?
The checkdisk you describe is a self-protection mechanism for Windows to see if there is something physically wrong with the computer disk. So, the larger the disk & more data on it, the longer this process takes.