I don't know Bullguard, so my apologies if it is a security suite that includes anti-virus and anti-malware.
Whatever you use, I would download, install, update and run full scans with two other utilities, Malwarebytes' Anti-malware, and SUPERAntispyware.
I don't know Chrome very well, but with both IE and Firefox, there are add-ons that can slow browser speed down, so that's another avenue you could try, an add-on elimination test on each browser.
When you check the Task Manager > Processes tab, click the CPU column header to organise the processes in order of CPU usage. Don't forget the option at the bottom of the screen to show processes from all users.
Are any particular processes using up a lot of CPU time? Disregard the "System Idle" process. If it is above 90% then that is normal.
I have a 15 month old PC used by all the family (Windows Vista Home Premium running on a 3Ghz AMD 4Gb RAM 250 Gb HDD system) and have a problem specifically with slow running browsers.
The browser (and this applies to Google Chrome, Firefox, and IE8.0) loads individual pages agonisingly slowly. Multiple tabbed browsing is no longer possible. There are no obvious firewall conflicts (i.e. problem still occurs when firewall (Bullguard 8.0) is disabled. Windows firewall is permanently disabled.) However, and notably, use of Windows Messener by teenage family is not noticeably slower. Other software seems to run OK.
Speed checks on the internet connection suggest that our line is delivering 3-4Mbps - no slower than used to.
One further piece of info which may be relevant. Windows Task Manager suggests that typically 50% of memory is in use.
I appreciate that this is an incredibly broad query but does anyone have any ideas as to how I might approach this? Suggestions as to what to look for would be gratefully received!!!!