I think you need to consider not just where to advertize but how to advertize. What is your USP? Are your prices competetive? Do you have any special offers?
If you have a site then use articles to build up traffic. Write hints and tips about maintaining computers, ideas on keeping up to date with virus software, anything relevant that your customers are likely to search for.
Best of luck.
Sharona B
Freelance Writer and contributor to www.nimdx.com a free information directory for online businesses