[Kymmy]

Sounds like one of three issues..

1# Virus/Malware (run a full scan)
2# Low disk space and RAM (PC will try to use disk space as virtual ram but that shouldn't effect PC on first start unless you have a memory error.
3# Somethings effected the size of your page file and dropped it down. Instructions to change your page file size to let the computer handle it is as below

Make sure that your virtual memory is set to "Automatic"

Right click my computer, choose properties..

for Win7/Vista then choose Advannced system settings, Performance settings, Advanced, Virtual Memory change and then make sure that the Automatically managed checkbox is ticked for all drives..

For XP it's.. Advanced, Performance Settings, Advanced, Virtual Memory change and make sure that System Managed Size is checked..

You will need to restart