At this stage of the game, it isn't readily apparent what is causing you to freeze up.
Did you turn off System Restore (deleting all restore points) ?
Let's see what we can do with the "Cat in the Hat" Calculatus Eliminatus method (ruling things out).
Get the free program Autoruns
Our goal here is to find out what all is set to run on boot, and see if we can get it down to bare minimum, meaning only what is absolutely necessary.
Here's a description of Autoruns (copied/pasted from the technet.microsoft.com website):
"shows you what programs are configured to run during system bootup or login, and shows you the entries in the order Windows processes them. These programs include ones in your startup folder, Run, RunOnce, and other Registry keys. You can configure Autoruns to show other locations, including Explorer shell extensions, toolbars, browser helper objects, Winlogon notifications, auto-start services, and much more. Autoruns goes way beyond the MSConfig utility bundled with Windows Me and XP.
To disable an auto-start entry uncheck its check box."
Do not disable your antivirus program. If you have a firewall program, do not disable that either. Anything else, temporarily disable using Autoruns. See if that helps your freezing up problem.
Just curious, have you looked to see how much of your hard drive is "used" and how much is "available" ?
My Computer, C drive, Right Click, Properties, will show a pie chart that tells Total Capacity of your hard drive, how much used, and how much available. If you don't mind, please let me know this information. I don't know how much of a packrat you are, or how many programs you have installed, but on a 4yr old computer, things do tend to accumulate. I doubt seriously this is the cause of your freezing up, but it's probable that your computer isn't as fast now, as when it was "new".
Also, have you looked to see if you have any hardware conflicts in Device Mngr. ? A hardware conflict is marked with a yellow circle with a black exclamation mark in it. Start Button, Control Panel, System, Hardware tab, Device Manager button. If there are any hardware conflicts, that category will automatically appear "popped open" and you'll see the tell-tale yellow circle with a black exclamation mark". If you have any hardware conflicts, please advise on what device(s). I doubt this is the cause of the freezing up, but it doesn't hurt to check.
More than likely, the cause of your freezing up has to do with something (or several somethings) running, that are using up alot of resources, which is why we're going to try getting you to bare minimum on what you allow to run on boot.
Since you froze up once you got back to "normal mode", that tells me that whatever is causing the freezing wasn't running in "Safe Mode". It's going to be a matter of figuring out what that is.
Are you using the latest version of Firefox? Do you experience freeze up when you use IE (Internet Explorer) also ?