Acer Aspire 5315-2326 Vista laptop slowing down

In the past few months my laptop has slowed down drasticly and I'm not sure why. Some examples:

-alt-tabbing between programs is slow
-changing directories in Windows Explorer is slow
-opening new tabs/closing tabs in both Firefox and Chrome is slow/mouse becomes unresponsive
-programs become unresponsive for a bit, happens often with Firefox and Chrome
-I lose mouse control for a bit

The above examples don't always occur but they do happen frequently enough to be pretty annoying. I run frequent virus scans via avast! and have never had any issues. I also use COMODO Firewall and keep both avast! and COMODO updated. I run Windows Update as new updates are available.

System:

-Acer Aspire 5315-2326 Laptop
-Vista Basic
-Intel Celeron 550 2.0GHz
-1GB DDR2
-1.5 years old
-more than 10% space is free on both HDDs

Questions:

1. I've never run a disk defrag, should I use the Windows one or pick up a 3rd party utility?
2. Is there a utility suite I can run that will check for and fix any issues I might have?
3. Is it possible this is due to a Windows update?
4. A fresh boot reveals a 750MB memory usage (out of 1GB) in the Performance tab of the Windows Task Manager, is that not fairly high? I only have an avast!, COMODO, DU Meter, and NetLimiter 2 Pro running.

Any help is appreciated, thanks!

 

10% free space isn't much and tbh 1gb RAM isn't really enough for Vista.
I increased mine (Aspire 9301) to 2 gb and it made a massive difference. That said Vista will run with 1gb but is slow to boot and a little unresponsive. 750gb usage sounds spot on for 1gb and I bet the HDD light is working (flashing) overtime as the pagefile is contantly written to.

Worst case scenario... you can always do a factory restore back to day 1 (which wipesthe hdd and your data) and start again. It's all available via Acer erecovery already installed

If you have ever tweaked or run registry cleaners etc then all bets are off and there may be problems with the operating system that tbh only a reinstall will put right.

However,

Defrag... Vista by default runs this process automatically unless you have disabled it. I doubt anything here is the problem.

I would recommend you first try and free up space by uninstalling any programs you do not use.
Uninstall or change a program

You can delete all but the last restore point (which takes up a huge amaount of space).
Delete a restore point

Open task manager and see what is running,
How to use and troubleshoot issues with Windows Task Manager

With 1gb RAM you need as litle as possible running. I use Microsoft security essentials and Vistas own firewall with a clean Vista install.
Brilliant... boots to desktop in around 1 min 30 seconds and that's to load everything including the sidebar, and running Aero. HDD usage is essentially zero as shown here. Open your "performance and reliability monitor" to see what is using a lot of CPU and disk capacity. This image was taken as I was typing this reply with this page open...

 

Yeah the problem is more likely in the components, I mean 2Ghz Celeron and 1GB of RAM is simply not enough to run Vista smoothly especially if it's been on for several months(OS tends to slow down during time because of installing/uninstalling of software, updates etc). I'd recommend upgrading to C2D CPU and to 2GB RAM and if that's not possible - downgrade to XP, it will run better than Vista.

 

The hard drive fragmentation is the main issue at this point as @Mooly mentioned

To defrag properly 25% space is needed on your drive to leave room for temp moving files while defraging

You need free space , and here is a link to an excelent thread that will show you how to free it up

http://forum.notebookreview.com/not...983-wheres-all-my-disk-space-going-vista.html

As both members posted your ram is an issue as well
2Gb total will work the best
It looks like your laptop can take 1GB modules and in searching for compatable modules I find that you use PC2-5300 667 Mhz type

This type is very common and inexpensive ,buy 2 1Gb modules