My Presario 700 freezes up at random times

Sounds like the following

Virus

Spyware

Devices or drivers are conflicting.

Hard Drive is failing

Step one

Disconnect the computer from the internet.

If this is the problem it is more than likley a virus or spyware

If it still freezes proceed to step 2

Step 2

Restart Computer in safe mode, do not connect to the internet.
To restart the computer in safemode turn on computer and press F8 continuosly until a screen of options comes up.
Select Safemode without networking

If this is the problem it is more than likley a virus or spyware

If computer still freezes up proceed to step 3.

For windows XP
Locate the My Computer Icon and open it. Locate Local Disk C: Or whatever harddrive that has windows installed
RIGHT Click it. It will then open a menu of options, select properties. At the top select tools tab. Click the check now button.
A new window will pop up, check both boxes and press start.
Another window will pop up select yes and restart the computer. Do not press anything and let it work.

Considering the age of you computer it is probably the hard drive in which case should only cost about $45 for another one. search for a harddrive that fits your model on ebay or another trusted site.
It is not very difficult to change the hard drive so dont panic.