Thank you for taking time to give me such detailed instructions, mchainmchain.
I am unable to do the mem test because the laptop has no internet connection. The model is Toshiba Satellite L20 with Service Pack 2, Intel Celeron 1.60 GHz, 256MB RAM. It has 37GB HD with 32GB free space.
However I did use the Toshiba diagnostic tool to check all the hardwares and they all passed, including the memory.
Device Manager did not show any yellow exclamation mark.
My husband bought this laptop about 7 years back exclusively for his word processing job. When he needs to send an email, he typed it out on this laptop and I take it with a thumb drive and send it through my Desktop, and this has worked well for the last 7 years before this mess happened.
Just now I tried to copy his email to my thumb drive using 'save as' and an error message came up and I was unable to do it. Then I used Windows Explorer, and it worked. After I have closed all the files, with no other programs running, I checked System Information. There it said: Total physical memory 256Mb, Available physical memory 27MB! Where did all the memory go?
Around the same time that this problem started with the laptop, my Desktop also slowed down markedly. I suspected some malware. But scan with Microsoft Security Essential yielded nothing, while scan with Super C Antispyware yielded only tracking cookies which I duly removed.
The Device Manager however has a yellow question mark on 'unknown devices'. Is that significant?
Any further advice will be very much appreciated.