XP on Inspiron 5160 showing signs of instability. What do I do?

Not sure just what is going on but my system or something seems unstable or something.  I hope this is the right area to post.

Yesterday it would only boot in safe mode (with networking).  Today, after fixing problem yesterday, it shut down with an error message that Problem detected and Windows was shut down to protect computer (although it did restart on its own after awhile).

Yesterday the Windows screen would come up but then it wouldn't boot and gave me a DOS type screen with choices.  It wouldn't boot normally or into last good one, but did boot into safe mode with networking.  I called GeekSquad just to ask about their services and was talking to a tech who said he thought I had a virus.  I could get online but their chat thing wasn't working.

I started using my Avast Professional to scan for viruses.  We disconnected since it was taking a long time.  It didn't identify any viruses but there were a bunch of things it couldn't scan.  There were a bunch of spybot S&D parts and I think Adaware (neither of which I use any more so maybe I should figure out how to uninstall them?) and then there were 3 ea in my email in and out boxes.  3 with the same in message and 3 with the same out message.  When I selected them it gave the option to repair which I did.

I then scanned with A2 anti malware but with definitions from June.  It only found one tracking cookie--low risk associated with Comodo firewall so I left that.

I shut down and then after awhile rebooted and it booted up normally.  Then I did update the A2 definitions and re-ran it and quarantined the low risk things it found--I think they were all tracking cookies.  And before going to bed I backed up everything using Retrospect Express to my external HD.

Today I turned the computer on and then was reading my email after checking for new email.  I wanted to delete some emails and I noticed that my external keyboard (a Microsoft "ergonomic keyboard" which uses a ps2 to usb adapter which I have plugged into an old powered hub) wasn't lit so wasn't on.  For months it is that way so I have to pull the adapter out of the hub and then plug it back in and then it is recognized. Tonight when I did it I got a STOP message on a blue screen saying that a problem was detected and Windows had shut down to prevent damage to my computer.

It said to check for adequate disk space (I have 1 GB RAM which has always been enough and I didn't have too many programs open at that time anyway--less than I often do) and plenty of HD space free.

It also said if a driver is mentioned to disable the driver or ck with the mfg for driver updates.  It also said to try changing video adapters and then it mentioned BIOS updates.  I think I'm running A07 which a tech updated to when he replaced the motherboard a couple of years ago.

The message after stop included the following which I don't understand:  0x0000007E (0xC0000005, 0x804E83B8, 0xF79BEA68, 0xF79BET64). It also mentioned that it was doing a memory dump and I could see the #s increasing. Then it restarted itself ok.  But I don't know why the 2 problems in 2 days and want to take action if possible to fix whatever might be causing these problems.

Other background of recent changes that may or may not have bearing on this.  I just moved a week ago and it was only Wed that my isp came back and was able to fish the cable out of the wall and set it up upstairs at my desk, after working off a splitter downstairs for several days.  Last night I finally connected my multi-function printer up to the computer, although I haven't hooked it up to the phone for fax functions yet.

I'm running XP with SP2 and the updates they have suggested except for SP3.  I just downloaded and installed more updates I think it was yesterday evening after yesterday's problems.

I'm using 2 hubs.  A very old Belkin 4 port powered hub which I originally used on a Mac and a newer D-Link 7 port powered usb-2 hub.  I had hoped to be able to get rid of the old hub with the new one but then I read that if one usb-1 device was connected all would be slowed to that speed.

The only other thing I can think of that might have affected things is that I use magicJack and on Thurs night when I went out, I pulled it out of the hub, hoping that the computer would then sleep while I was out. But it didn't sleep, it was still up and running when I got home hours later.

I have not plugged the magic Jack back in since then. And Thursday was the first day I think that I had been able to use it at the new place since with the makeshift set up downstairs the only peripheral that I had connected was my external mouse.  It worked fine apparently and I had a nice conversation with a friend using it.

I'm usually fairly careful about which websites I browse and don't frequent the high risk kind as far as I know.

I did get a warning from Avast a few days ago while downloading email that was confusing. It was a heuristic warning and it looked like maybe there were 2 emails that were suspicious but I only got info on one and it was from a group that I trust.  I think I said to download it.  I don't know for sure there  was a 2nd one--I never got any details about it.  But that was before I ran the scan and then repaired them after the problems yesterday.  And that didn't actually find any viruses--just some that it wasn't able to scan and it was something about fonts in the messages that I didn't really understand.

The computer is about 4 1/2 yrs old and had the HD replaced after about 6 mo when it crashed. About a couple years ago the motherboard was replaced because the ethernet connector was loose and intermittent. The CD/DVD drive was also replaced at that time and the BIOS was updated I think to A07. So, although it seems to be working now, I'm concerned with both problems and whether there is something else that needs attention to avoid further problems.  I'm not a techie and get real nervous when my computer acts up and 2 malfunctions like this in 2 days is scary and makes me wonder what is going on.

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Inspiron 5160, 1 GB RAM, XP SP2 with updates, Firefox 3.0.5, Eudora 7, Comodo firewall, Avast Professional anti-virus, A2 anti-malware.