How can I make my computer faster without installing new ram because my computr is still under guarantee

You are able to upgrade parts of your computer without voiding anything, but they will not cover the new parts on the original ones.

As for making it fast without adding ram or a high clocked CPU, have you deleted files you don't need, cleaned it with disk clean up (ccleaner is better, gets more stuff), defraged the drive?

And also, kill some of your start up processes. I don't know which OS you are running, but go to run, type in msconfig, and choose the second to last tab, startup. There should be a list of everything that starts up with your computer, and most of them you don't need. Ex. AIM, iTunes, Quicktime, Adobe, firefox/IE, uncheck those types of things first. Also never uncheck anything that has system32 in it

Try to optimize your computer

1. delete all the junk file like temp , %temp% , prefetch.
Start > run > type Temp > OK . Delete all the files ( same as %temp% , Prefetch )
2. Run disk clean up.
Start > program > Accessories > system tools > Disk clean up.
3. Increase virtual memory.
Go to my computer properties > Advance > Under Performance, click on the Settings button > Under Virtual Memory, click on the Change button > Here is where you decide the amount of Virtual Memory that you need to increase. Try playing around with a few hundred megabytes above the assigned amount.
How to Increase Virtual Memory in Windows XP | eHow.com (http://www.ehow.com/how_2282429_increase-virtual-memory-windows-xp.html)
4. Disable all the startup itemps from msconfig.
Start > run > type msconfig > ( Startup Tab ) System Configuration Utility.
How to Safely Disable Startup Items Using Msconfig | eHow.com (http://www.ehow.com/how_4831800_disable-startup-items-using-msconfig.html)
5. run Disk defrag.
6. Scan your computer Weekly bases with using any good antivirus and Spyware removal software.

This link offers suggestions to help "speed" up computer
-Look at the 3rd and the 5th post
https://www.askmehelpdesk.com/computers-beginners/frequently-ask-questions-about-computers-233870.html

You will notice an increase with applying suggestions offered

From there, add some more RAM when possible