We would have to know more information about your system:
When did the problems become a major difficulty? Memory installed, Age - How old is the computer, Operating system, Hard drive capacity, age, and free space., video Graphics, Connection to the internet... etc. Can you go to Start->Control Panel->System->Hardware->Device Manager. If so, do you see any red, gray, black or yellow flags or alerts about any of the devices?
Do you have the restore disk set from HP? If not, can you afford the cost of ordering that set from HP (the machine must be registered with Hewlett Packard), if we feel it would be helpful to restore your system? Do you have all your data backed up?.
You might also want to buy a container of canned air to blow the dust, dirt, and fiber out of the CPU, CPU fan, and other components if there is a visable amount inside the case.
If we have your HP product number, we can look it up on the HP web site... But we can tell most of what we need to know from the ID you have given us.
Do you have a budget for making a few repairs or replacements if that becomes necessary?