>>>I think some virus or Trojan got into my computer and now I only see one drive C: whereas before I had drivers D: and E:. The drive C: only shows very little space left. When I run the Windows Security Essentials it says that it cannot clean the computer and recommends downloading the Standard System Sweeper from some site. Does this sound as legitimate?
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>>There is such an app from Microsoft Connect..although I've never tried it.
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>>This of any help?
>>http://www.technobuzz.net/fix-missing-drive-in-windows-7/
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>I am looking at my Task Manager and see many, many instances of SVCHOST.EXE running. Also I see the process PUAZEE.EXE that seem very suspicious. Do you know anything about these two?

The SVCHOST.EXE's are probably OK as it's a generic host process name for services that run from dynamic-link libraries - although some trogans disguise themselves with such.
http://www.howtogeek.com/howto/windows-vista/what-is-svchostexe-and-why-is-it-running/

As for the PUAZEE.EXE - I'm not 100% sure about that one... but seems like I recall hearing about a virus with that name that screws up your explorer.exe - and based on your current situation I'd say this might be the culprit. Wouldn't surprise me if you went to taskmanger, killed it..and then it starts back up again on it's own (probably via one of the svhost.exe).