My desktop is an Optiplex 755 and it has 4 gigs of memory and running on Windows XP.  The My Computer properties show 3.23 gigs of RAM. I understand Windows XP cannot utilize the full 4 gigs of RAM which is fine with me. 

The computer slows down often and I assume it is because of memory issues and I could be wrong. If I restart the desktop it works fine for few hours. Generally if I dont restart once a day, the pc is extremely slow. At times I have to restart twice a day.

I dont know if this is a memory problem. I downloaded FreeRam XP pro which is supposed to manage the memory. This software shows 1590 mb free out of 2048 installed. It is not showing the full 4 gigs for some reason. This leads to me to believe that the computer does not have access to the full memory. I have a laptop which has only 2 gigs memory and it can go on for nearly a month without requiring a restart. I use pretty much same programs/softwares in both the desktop and laptop.

How do I determine what is the problem. Is it memory issue or something else?

Any pointers is highly appreciated.

Sincerely
Arvind.