Windows 7 - High disk I/O causing slow startup / and a weird RAM problem

Hello everyone
I have 2 problems
please help
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(1st)
I have a problem with my Windows

my start up time is so big from a while and I don't know why
I have some nice widgets that showing to me the CPU utilization and RAM utilization
also shows me disk usage

I find that my CPU is always 2 to 15% and my RAM is 18% or something (While start up)

but I find that my disk usage graph is always full and stays like that for a while

so that I can use my PC normally after something like 4 minutes from starting the PC

is there's a utility to know which program is using the disk that much ?
or how can I stop that ?

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(2nd)
I have a 6GB DDR3 RAM and I also have Windows 7 64bit
which is supposed to be able to address the 6 GB fine with no problems

suddenly I found out that in my system overview the memory is
6GB (2.00GB usable)

once before it was 4GB usable

and don't know how solve that :S

BIOS Settings are fine (I Suppose) cause I can't find an option to limit the amount of RAM or something

so please help
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Any help would be greatly appreciated

If you use the clean boot and follow the directions carefully, you will be able to determine the source of the problem
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7

Okay thank you for that

But what about my RAM problem

One step at a time
One of the start up programs may be malfunctioning or even have a virus. When you do the boot, look at ram usage, too.

One step at a time.
We can do a memory test later. But do the boot first.

Actually now the booting time is a bit faster
Now I will try to enable the start up items to see what happens
BRB Rebooting 8-|

Take your time. Best to do it right, rushing will not help
Do an anti virus scan.
Download and scan with malwarebytes. Do the full scan.

Back. Start Up was too slow
Now I think the problem is in a start up item
but I need to do something that makes my system faster than that -Like a fresh install-
Anyway I will download the software you mentioned and will keep you posted
and thank you
Rep+

Thanks Buddy
The software will check for virus and other malware.

Till the scan finish
How can I solve this RAM issue ?

The two scans are checking for virus and malware. If some are found all your problems may be solved.

So with the clean boot. It went faster. Did you put the programs back a few at a time to determine what caused the problem?