why are some computers so slow?

The processor may be slow and the RAM may be small..Try upgrading your hardware.. Virus may also slow down your system..Scan your system for viruses using any antivirus of your choice..I use Avira AntiVir and it works quite well.. Also try to fix registry and fragmentation problems in your OS..These slow system performance..I use TuneUp Utilities for these.. Lastly, try to tweak your system..Reduce visual effects..Turn off unnecessary functions and processes in your computer..

Computers are very tricky and I do not know if anyone knows why they are so slow and viruses can slow down your computer,but then you have to wonder how you got the virus in the first place,and maybe you do not have enough hard drive space,but I hope you figure out the problem,and get your computer back to the speed it should be at,so that way you can do more things without it freezing or being slow on you,Happy Posting.

Reasons for slowing down of PC is of many reasons. One can give you correct guidance only after looking your PC. Virus is not the only reason for slowing up of the PC.. Try to give more details, so that one can help.. all the best...

if im in your case i will format my computer to get a fresh new start.. if its still slow then you have a hardware problem.. better check your processor and RAM or DDRAM.. you might need to upgrade your hardware.. hope this will help you.. :D

check your specification of your computer check the proc, memory etc defrag your HD give some free space on your C drive reinstall :D

Sometimes the OS system files become tanted. You might think the virus is gone, prob. is but something else is on the computer. I know that there are programs that will be useing you memory behind you back, and run a fake windows that looks the same but wont tell you what going on. Like a windows emulator for windows. You computer would be like half a computer then but you wouldn't know why. It could just be over heated as well but i doubt it.

Well its not only viruses and stuff its the hardware, it might be damaged. And that with pop ups was probably an adware try to do virus scan with several programs.

The most easy and fast method ----reinstall the system.

it have lots of reason a virus is one. or the computer hardware needs boost up.