Old computers slowing down

[Josquius]

Back at my parents. Very very bored.  As in the prior times I visited I'm experimenting with my 10 year old computer to see what I can do with it. As it turns out very little.
I'm trying to deduce exactly what it is that has made this old computer slow down.

* psychological? I have become used to newer smoother systems and now what was normal 10 years ago doesn't count it?  - I do not think so. Regular usage used to be smooth.
*updated requirements -  a part of it. An annoying part of it. YouTube used to work fine on this computer.... but now it fails miserably at it. In an attempt to optimise their site youtube have made their site so demanding that my computer no longer cuts it?
*accumulated dust, etc....- possible. Though it seems pretty ok there.
*hardware wear- now there is my question. A big source of mystery.
From what I gather:
Hdd - shouldn't slow with a age (if reformatted). Works or doesn't.
Ram- some stuff I've read suggests issues may lie there over time with things like static. Intriguing.
Processor- some I've read says no way does this get slower with age. Considering I've not redone the heat paste though.... I suspect it may be?
*hard drive fragmented, reformat, reinstall- come on. First thing I tried, obviously.  Currently computer is stuck with linux and won't boot from a cd. Bah.

So. Does anyone have any experience with this sort of thing?
Any idea what could make an ancient computer so much slower than it used to be?
It has gotten so bad that I can do nothing on it.

[Phillip V]

Uninstall old/unnecessary software/programs and then check Task Manager to see what else is running.

[DontSayBanana]

Back at my parents. Very very bored.  As in the prior times I visited I'm experimenting with my 10 year old computer to see what I can do with it. As it turns out very little.
I'm trying to deduce exactly what it is that has made this old computer slow down.

* psychological? I have become used to newer smoother systems and now what was normal 10 years ago doesn't count it?  - I do not think so. Regular usage used to be smooth.
*updated requirements -  a part of it. An annoying part of it. YouTube used to work fine on this computer.... but now it fails miserably at it. In an attempt to optimise their site youtube have made their site so demanding that my computer no longer cuts it?
*accumulated dust, etc....- possible. Though it seems pretty ok there.
*hardware wear- now there is my question. A big source of mystery.
From what I gather:
Hdd - shouldn't slow with a age (if reformatted). Works or doesn't.
Ram- some stuff I've read suggests issues may lie there over time with things like static. Intriguing.
Processor- some I've read says no way does this get slower with age. Considering I've not redone the heat paste though.... I suspect it may be?
*hard drive fragmented, reformat, reinstall- come on. First thing I tried, obviously.  Currently computer is stuck with linux and won't boot from a cd. Bah.

So. Does anyone have any experience with this sort of thing?
Any idea what could make an ancient computer so much slower than it used to be?
It has gotten so bad that I can do nothing on it.

Well, whoever told you HDDs don't slow with age told you wrong.  HDDs are kind of like "record players" that work by spinning the platters under a magnetic "needle."  Those motors can wear down with age (keep in mind, they're frequently spinning at either 5,600 RPM, 7,200 RPM, or 10,000 RPM in their prime), slowing them down by increasing the drive's seek time.  On the software side, you can cut down the seek time somewhat by defragmenting the hard drive (putting as much data in consecutive blocks as possible, making it less frequent that the drive has to spin up).

Most of the speed culprits are software, though.  Look for things like "iTunes service" that may start on boot and chug a ton of memory, even though you probably don't need them as you're not using this as your primary daily computer.

[Norgy]

SSDs are not much better and have a limited lifespan. I just had my first one die on me. Poor baby.

[Josquius]

As said last time I was home I reformatted my C drive and started all from scratch, so bad software, etc.... isn't an issue. It must be the hardware itself going to hell.
Its not a big technical issue I need to solve, its just something I use on the rare occasion I'm visiting home. Though I do have a big curiosity in why its so bad,