From time to time I find these poor machine callously thrown away (which I rescue when I see them) most of the time its been thrown away because of the lack of performance.
I'm going to assume your operating systems are made by Microsoft .
1. Is your hard drive too full? over time microsoft's updates archive undo files and over time can take up a lot of space. the symmetry of the swap file gets so fragmented it will spend time seeking for the next block of the swap file to write in that it takes processor time away from the rest of the system.
2. Aging hard drives. Hard drives are mechanical things (with the exception of other technologies like SSD) . that has metal oxide coatings on spinning aluminium platters. After some time, the coating delaminates from the platter causing a void. If the checksum recording of that sector is still intact the s.m.a.r.t. system that is built into the firmware of the hard drive will take over and reallocate that sector to an area called the engineering sectors that are located outside of the drive partition. once the engineering sector area is full, the hard drive will post a warning message (if the bios is turned on to hear the messages) at boot up time that hard drive failure is imminent, and should be replaced.
3. Memory speed. most of the consumer mass market was loaded with slow memory. Always try to use the fastest memory possible for the machine and never mix memory speeds. It is also recommended to max out the memory as the capacity issues can slow performance.
4. Turn off hardware acceleration in flash. Most of the streaming issues are caused by invalid hardware calls in acceleration mode. Internally, the computer handles the error and switches to software mode. but the system is doing that on the fly, and so the extra processing leads to poor real time performance. The only other thing that would cause poor performance is the operating system itself.
5. Replace windows with linux. After the years of supporting them, I don't any more because 99% of these machines I rescued and put Linux on them made them work just as good (and sometimes better) as a low end current machine. I recommend Xubuntu for these older machines. Malware and viruses are very non-existent on that platform.