OK, look, I'll just make do without the RAM etc for now.
Couple of things to try.
Rename the HijackThis installer file, to something like "marliny.exe" and then see if it might install.
No luck? Time for a check disk. Right click the "C" drive of "my computer" in the start menu (if you have one listed there.) Select "properties" then "tools", "check now", tick both the checkboxes.
Restart. This might take an extra half hour or so for the check to run and the logon screen to come up. (I'll be in bed by the time it would be finishing, BTW. Others might well come and help.)
Following this try installing HijackThis again.
Other ideas: Download
Cureit from the good DrWeb. This is a standalone virus/malware scanner/cleaner. No installation; it will run from the download location. (I suggest the desktop.) Run it immediately after downloading it. It can't be updated, so is really only good on the day it is downloaded.
Hope something here works. I'm admittedly not very expert, but reasonably proficient, and starting to run short of ideas.
BTW, is the computer regularly updated from MS Update? Can you visit the site?
Really want to know this.
Can you view
this page symptom-free? (Explanation on the page.)