Run a scan with HijackThis. Check the following and hit 'Fix checked'
O20 - AppInit_DLLs: dhpmnb.dll
Reboot to safe mode ->
Restart your computer.
When the machine first starts again it will generally list some equipment that is installed in your machine, amount of memory, hard drives installed etc. At this point you should gently tap the F8 key repeatedly until you are presented with a Windows Xp Advanced Options menu.
Select the option for Safe Mode using the arrow keys.
Then press enter on your keyboard to boot into Safe Mode.
.
Show hidden files and folders
Click Start button, then go to Programs, Accessories and click on Windows Explorer.
Select the Tools menu and click Folder Options.
Select the View Tab.
Under the "Hidden files and folders" heading please check Show hidden files and folders.
Uncheck the Hide protected operating system files (Recommended) option.
Click Yes to confirm.
Click OK.
Find and delete this file (if present)
c:\windows\system32\dhpmnb.dll
Reboot normally, attach fresh hijackthis log and tell how things are running now ?