a) Clear out all temporay files and folders -- use Crap Cleaner click here
b) Scan for malware spyware and viruses --Free Anti Spyware :-
Superantispyware click here
Malware removal tool click here
d) Pagefile (Virtual Memory) -- Rght click MY Computer - select propeties - Advanced tab - Performance - advanced tab - Virtual memory click change, you can put the page file on a different drive (if you have one), click custom size and set Initial size to one and a half times the amount of memory you have fitted i.e. 512MB memory = set to 768MB, set maximum to double your memory amount i.e. 512MB memory = 1024MB click ok.
If your hard drive is full and there is not enough room for the pagefile this can slow down, freeze or even cause the PC to crash (restart).
click here for how to move USer folders.