Windows 7 Multiple Problems

Hi, I have a Dell Inspiron 545 64-bit system. I have 6.00 GB of RAM. A couple days ago, my computer suddenly became unresponsive. I left it alone for awhile to see if it was just a lag, but it remained unresponsive for 4+ hours, so I performed a hard restart. I logged into my profile as normal, and it worked fine for a few minutes, but then a low memory notice popped up. It asked me to restart all my programs to help restore memory. (This was odd because nothing like this had ever come up, even when I were to run several programs at a time.) I subsequently went to close Chrome (the only thing I had open), and when I clicked on the X to close it, the computer froze again. I did a hard restart and the same thing happened two more times. I eventually thought there might be a shortage of space on the disk, so I copied much of my music and videos to my 2TB external drive, and freed up over 290 GB of space. This allowed me to use the computer longer before the memory low popup showed itself. It froze again, but this time, when I restarted it, I ran a Malwarebytes scan, and the memory low popup stopped me about two hours into the scan. Although it was incomplete, it had scanned a lot and found nothing. I am typing this from my computer now, and I have 5 tabs open in Chrome and it doesn't seem to be slowing down or freezing. But, I am almost positive that if I were to open WMP or Itunes, or something similar, the computer would freeze up. I don't know what to do about this except maybe install more RAM or play with the virtual memory, but I don't know why these problems randomly started. I have never had issues like this before, and I've had the computer for 3+ years. If anyone has any idea what the problem is, I would greatly appreciate some assistance.

Thanks,
Steven