A month or so ago there was a trojan, I believe, that disallowed the user to access the Yahoo! and Google search engines, turning up search queries -> "Page cannot be displayed."

If anyone has any information to solve this problem, thank you.

Hi toDo

Perhaps you are thinking of this one?
Trojan.Qhosts
http://www.symantec.com/avcenter/venc/data/trojan.qhosts.html

That link also has the removal tool located here:
http://securityresponse.symantec.com/avcenter/venc/data/trojan.qhosts.removal.tool.html

All the major Antivirus Programs and the AntiTrojan programs now detect this. Have you run a scan with an AV? If not, here are a few free online AV scanners available.

Panda's Active Scan
http://www.pandasoftware.com/activescan/com/activescan_principal.htm

Trend Micro (PC-cillin) - Free on-line Scan
http://housecall.antivirus.com

RAV Antivirus Online Scan
http://www.ravantivirus.com/scan/

Besides the QHost trojan there have been a number of new ones discovered recently. The symptoms you describe do sound like you have some type of trojan or browser hijacker on your system.

Download one of these (free) Antispyware scanners, if you do not have one already. If you are a novice with these types of programs I recommend Adaware first as it is a little easier to understand and use.

It is critical that you have also gotten the latest updates for the software (Adaware last updated Nov. 3) and the correct settings for scanning. Here is a short tutorial with easy to follow screen shots on how to update and configure your settings before scanning

Adaware
http://www.lavasoft.de/software/adaware/

Adaware Tutorial Updates & Scanning
http://forum.gladiator-antivirus.com/index.php?showtopic=8050

Spybot Search and Destroy
http://www.safer-networking.org/

If you have any questions, or need any futher help, please post back here after running those scans