Yup - replace the battery and it should fix the clock, it also may improve things since you will be able to save the proper BIOS settings.
If you have a copy of either Windows Vista or Windows 7 (as they are both the same operating system) that has been previously installed, all that you must do is call the phone number and do a manual activation. It works every time, even with OEM product keys... the only issue is when someone does something incorrectly - for example, when they ask you how many computers this is installed on.. you better say "one" or you may have problems with that key. Also, don't attempt to reactivate the old computer with the same key
If these lock-ups are random and CPU percentage is low than turning down your visual settings will not increase performance. I would suggest that you a) install a new CMOS battery (which may be just under one of the small covers on the back, or the keyboard.. if you're lucky); b) install the non-microsoft drivers for your GPU and motherboard chipset. Forexample it may be a Radeon Xpress 1150 IGP.... the driver will probably supply both the video and motherboard chipset drivers.
If something is botched up with the MS drivers it could lead to system confusion