You just need to tell me if you have like another Windows at your machine and if have seperate partitions as that way can tell what to do. I can tel you that you can use external hard disk to put all of your files on or CDs as well before doing the install of new windows on yoru machine. I hope that you have more then one partition as at the other partition can put files and more improtant data taht you don't want to lose. You can install Windows and put on one partition that will be the partition taht can use and i recommend have like over than 100 GB of space at that partition to make the operating system work. I hope that will work and windows can't make you lose files if make the Hard Disk partitioned into few partitions and take care there.
pls how can i install new windows without losing my files and pragrammes on it
If this is a new version of Windows you want to install, you can attempt to perform an inplace upgrade. If you do a clean install, you will wipe the partition, format and write new data.
If you care about your data and you have the installation software, I always recommend a clean installation. It may take longer, but a clean running version of windows is the way to go. Its not common to have a poorly running Windows system and expect the upgrade to make it run better. If it runs poorly now, dont expect any different after the upgrade.