here are replays of me playing against zerg and protoss computer. i still cannot win if i try to go beyond mid-game tech, since the computer will out macro me without fail.

any tips/advice will be greatly appreciated. thanks in advance.

Before I comment on your games, I'm going to let you know that TvP is one of the WORST matchups to practice against a computer. This is because the computer always goes 3-gate zealots, without getting either a forge or a core which you basically never see from any competent player. Hence the only way to properly practice beyond their initial rush in that matchup against a computer is to wall in and abuse the crappy zealot AI. FD and siege expo, the standard openings, are almost impossible to practice.

That said, I'm going to say right now that you should watch some pro or at least high-level semi-pro play. Modern Starcraft is no longer a game you can really hand-wave your way into a decent level of play. Even lower-level play requires a fair amount of game-sense for all races and all matchups (not just the race you play), so learning some from higher-level play is fairly crucial for advancement.

Comments after watching your replays:
1) You scout very early. As stated, watch some high-level play and see when they scout.
2) You use infantry vs. Protoss. As much as the stupid Protoss AI forces you to bunker up and use infantry, don't. Infantry are just not cost-effective against Protoss, especially when psi-storms and reaver scarabs are being thrown around, and can kill 10+ marines, medics, or firebats at once.
3) Conversely, against Zerg, you should be sticking fairly heavily to infantry, even into the later stages of the game. There's no reason you should be floating your barracks around in that matchup unless you're trying to reposition them.
4) Practice, and get faster. You have an APM of 40. While many people say that APM does not matter, APM that is low can hamper the rate at which actions are being performed. In order to play effectively, I'd say a minimum APM to work with is 100.

Honestly, I'd comment more specifically, but given how much your play should change after watching some pro-play and basically increasing handspeed, its not worth commenting right now.

i've actually watched a lot of pro starcraft. in fact, what motivated me in playing sc again was a person linking me to some pro matches on youtube.

but yes, playing against computer certainly does not develop good tactics for me. all i know is that if you park a bunch of marines at their entrance, they'll stop teching and try to push you out, which they won't, because they won't tech past marines/zerglings+hydras/zealots.

at this point playing against actual people is hard, simply because i cannot get b.net to work at university (where i usually play, since i spend all day there anyways). apparently my school's server blocks a particular port that b.net needs.

anyways, here's two more replays. i decided to try out zerg for a bit, so you can all behold my terrible mutalisk micro.

In that case, review some build orders carefully that pros use in games. Conventional TvP goes straight into Refinery and Factory with the Barracks, and usually doesn't get more than 5 marines, so there's no reason to go straight marines the way you did either way.

Well, there's a way to bypass that network port restriction using chaoslauncher.

Do play on bnet, you can't learn much from playing against computers

I also recommend going to SC2GG chat and asking around for people to play.

Don't be intimidated. Most people are pretty bad, including myself. Many of us are intimidated by higher level play so a lot of us are very noobish XD