Random mouse lag, unresponsive, slow. Please help.

If you do all this stuff, and the problems still persist:
I would change to a non-asus motherboard.
But here is a bunch of things that will usually help you.

Actually, 4GB RAM is quite a bit, when you use it at the intended speed....
Unfortunately, the default power settings dumb-down the possible speed of the computer.

Start> Control panel > look in the upper path bar, click on the arrow ">" after "control panel."
this opens a drop down menu
Then click "All control panel items"
Click: Power Options
Click: Show Additional Plans
Click: The arrow, check the box that says "high performance."
Click: Change Plan Settings
Turn Off Display: Never
Put Computer to Sleep: Never
Click: change advanced power settings
Hard Disk : turn off hard disk after: Never
Wireless adapter Settings: power saving mode Setting: Max Performance
Sleep: sleep after: Never
Allow Hybrid Sleep: Setting: Off
Hibernate After: Setting: Never
Allow Wake Timers: Setting Disabled
USB Settings: selective suspend setting Setting: Disabled
PCI Express Link Power State Setting: off
Display: turn off display Setting: Never (turn off monitor manually if desired)
Multimedia Settings
When sharing media : prevent idling to sleep
When Playing video: Setting: optimize video quality
Now: Click "OK"
Computer> system properties > Now open the Device Manager
Click On: mice and pointing devices ">" click on the arrow
Double Click on HID complaint Mouse
Click: power management tab
UN-check the box that says: "allow computer to turn off this device to save power"
Now open all devices on the list, and turn OFF all power savers, for every device, as above.
Now Click " OK"
Antivirus: set for "multimedia mode."
This prevents updating from interrupting your media. If you do not have an antivirus with this feature: get a different antivirus.
Set ALL updates to: manual. This prevents an update from eating resources that you would otherwise be using.

Free antivirus from internet: I do not recommend that you install any "free" security tools.
I do not recommend installing "cleaner," "sweeper," "driver helper,"or any free junk from the internet.

Avoid any download which claims to "fix" your computer.

I recommend that you use a professional all-in-one security application - not a free download.

Please consider, when you install multiple security programs, they can conflict with each-other. That's why you should use "all-in-one" professional security.
Restart the computer
Open Bios
Turn off Cool and Quiet (if AMD processor) Save and exit bios settings.
Restart Computer
Problems should be fixed now.

Before you do anything: backup all your files onto a DVD, or USB stick, etc...
No, I don't recommend updating the bios.
Instead: change the motherboard.
After you change to a non-asus board, you may find that you are much happier.

Same issue as you budd, i tried even more stuff nothing helped to eliminate the issue, gonna try replacing all parts 1 by 1 to find what is causing it.

Push control alt delete.
Open the task manager.
Look at the CPU usage.
If the CPU usage is running really high, try to look (click processes tab) and see which process is eating so much of the processor.

It could be a malware program...or it could be an application (like Chrome) which is overflowing the memory or processor.
I would try deleting all memory-hog programs...like Google Earth, etc...

Also: installing a bunch of "free" stuff from the internet...."free" security programs which conflict with each other.

I have ASUS Motherboard P8Z68-V LX and started to experience keyboard/mouse lags for almost a couple of months now. It's getting more frequent lately. I have swapped multiple keyboard/mouse pairs without luck. I am suspecting its a board/hardware issue. This board is about 5yrs old and discontinued.