Computer began lagging this week.

[a3soggetti]

Will driving a car with almost empty tank damage fuel pump on a second day? No.
But, eventually will.

So then... how do I determine what's gone wrong and how to fix it?

[Broni]

In many cases, there is no obvious solution, but you must start with getting your computer into "correct" state.
With your hard drive size, you'll need around 11GB of a free space, and we'll go from there.
That's one of the reasons, you don't have Restore Points - there is no space for them.

[patio]

Hard Disks:            C:  74.3GB
Hard Disks - Free:     C:  2.9GB

This is probably a big part of the reason...Windows likes approx. 15% free space which you are well under...especially for a laptop.

The amount of free space has been that low and lower before and this problem has never cropped up.  What makes this time unique?

I cannot answer that but i can guarantee that if it's left this way your issues will continue...

[programming_pat]

I just remembered that one day at the beginning of this week, after interrupting my computer's screen saver, there was a pop-up message above my system tray saying something about the page file.  Don't know if that's relevant at all.

this pop-up message basically means that your memory is running out, and windows creates a file on your hdd and uses it as virtual memory

[a3soggetti]

In many cases, there is no obvious solution, but you must start with getting your computer into "correct" state.
With your hard drive size, you'll need around 11GB of a free space, and we'll go from there.
That's one of the reasons, you don't have Restore Points - there is no space for them.

Okay, at this point I have about 13 gigs free.  I defragmented last night.  Lagging persists.  Do you have any suggestions about what I should do next?

[Broni]

Next thing to try is to uninstall current sound, and video drivers, download, and install fresh copies.
How is CPU usage in Task Manager, while playing media?

[a3soggetti]

Next thing to try is to uninstall current sound, and video drivers, download, and install fresh copies.
How is CPU usage in Task Manager, while playing media?

It's pretty inconsistent.  A while ago I tried watching a YouTube video and it changed irregularly between about 60% and 90%; if I tried to do anything else at the same time, it would spike up to 100% and keep bouncing around 80-100%.  The video, of course, was really laggy in the way I described before. 

Just now I opened iTunes and tried playing an mp3; at first usage was hovering between 70% and 100%.  After 30-40 seconds it dropped to around 30% and stayed around there (the song was clear!) until I opened Firefox again, and then it spiked to 100% and stayed between 60% and 100% for a while.

[Broni]

This is not normal. Can you check what process is mostly responsible for high CPU usage, during those spikes? Look at CPU column, not memory usage column.

[a3soggetti]

This is not normal. Can you check what process is mostly responsible for high CPU usage, during those spikes? Look at CPU column, not memory usage column.

It's not clear that there is a single most responsible process, at least with mp3s.  After experimenting I decided to copy the screen before, during, and after playing a couple of mp3s and then again watching a video.  For instance with iTunes: after the program was open, in the CPU column, System Idle Process had 83, iTunes had 12, a process labeled System had 3, and Firefox had 2.  During playback of one of the mp3s, System had 33, iTunes had 17, explorer.exe had 17, agrsmmsg.exe had 17 and firefox.exe had 17.  During a different one, iTunes had 60, task manager had 20, and System had 20.  During another, LastFM.exe had 38, iTunes had 31, System Idle Process had 25, and System had 6.  After that I disabled LastFM and tried another.  This time iTunes.exe had 99 and nothing else was eating the CPU.  Watching a YouTube clip, Firefox was definitely the only thing really doing much, but there was still lagging and CPU usage was between 50 and 75%.

Just now I tried Windows Media Player on some of my mp3s.  The CPU usage hovered between 34-56% and still lagged, with WMPlayer having between 7 and 34 in the CPU column... and everything in between.

What does it mean?

[Broni]

This is really puzzling.
Obviously the lags are caused by high CPU usage, but why do those programs use so much resources?
What are your computer temps?

[a3soggetti]

This is really puzzling.
Obviously the lags are caused by high CPU usage, but why do those programs use so much resources?
What are your computer temps?

Using SpeedFan, I found at startup the CPU was at 45C and the HD at 35.  The login sound lags as always.  A couple of times during startup, the CPU usage got up quite high and the CPU temperature rose... a couple of times to 50 and 51C.  HD remains at 40C for a while and climbs at most to about 46.  CPU stays between 47 and 49 mostly, only climbing higher if usage is high for about a minute or more.

Should I try uninstalling and reinstalling the sound and video drivers as you said?  What would be the most convenient way to do that?

Also, thanks for continuing to help me!

[Broni]

I found at startup the CPU was at 45C

This is pretty high for idle CPU.
This is what I'd try.
Turn computer off.
Open the case, and clean it well inside using compressed air (DO NOT USE VACUUM CLEANER!).
Keep case open, get house fan, turn it on, and point it toward open case.
Turn computer on, check temps, and see, if lags are still there.

[a3soggetti]

It's a notebook.  Er, carry on anyway?

[Broni]

Ooooooops...

[Broni]

My brain is pretty empty right now, as for what else to try. I don't like those temps, that's for sure.